Relative burned through funds and now mooching

He could hurt her.

Be prepared that when the time comes you may need to fight him in court to remove him and his belongings from the house.

This is absurd of course the door can be rekeyed. Contact a security company—they rebuilt Notre Dame using 11th century technology so I think despite the absurd awe you have for your father that you can find another security expert who can make a new lock.

I understand everyone's anger - it's so frustrating to read all the things this dreadful man has done and is doing, but it's YOUR MUM that is the only one that can really do anything - and she doesn't want to. So I think your only recourse is to grey rock your mum, every time she complains about him overstaying or spending her money or whatever, all you can do is tell her that you've told her what to do, but she won't, so she just has to put up with it.

Keep a watching brief, but as your mum has capacity, there really isn't anything you can actully DO about the problem, other than keep an eye on what he's up to. Your mum is just going to thwart any attempts you make to get him out or keep him out, and as she's the one moaning about him she must be getting something out of the relationship.

Legal advice as to how to avoid him setting up home in her house, but I'd guess if she leaves it to you and your siblings you can force him out when she's gone. Anything else - well, she's a grown woman and in charge of her own life.

It sounds as if your options are limited OP unless you find evidence that he's using her home to conduct criminal activity from - that would trigger the cuckooing framework and the police would get involved:

www.devonsafeguardingadultspartnership.org.uk/exploitation/cuckooing/

Or actively stealing from her / financial abuse: https://www.lawsociety.org.uk/topics/blogs/close-to-home-spotting-elder-abuse

In the absence of evidence I'd be making an inventory of her valuables (photographing etc) and checking at regular intervals that they're still there. It might be helpful if he knows this has happened as a preventive measure.

If he isn't eligible for benefits, that would suggest a bank balance of £16k+ - I would wonder if he is just too proud / above all of that sort of thing mind you. (In his own head)
I hope this freeloader gets his comeuppance.

Get him out !

as for where he can live, there is an old thread on MN where a middle aged man was about to lose his private rental, long story short he is now very happy in his social housing flat, for the over 55's. somewhere in Bristol I believe.
Apparently there are parts of the UK where the over 55's flats/bungalows etc. can be found without too much difficulty esp as your Uncle will actually be homeless once he moves out of Mum's home.

and yes he may be able to claim benefits and that would help pay the low(er) rent if social housing.

If I knew how I would search for the thread but don't know where to start. Yes the difference is that this man was working ( in prob a min wage job ) however your uncle will be expected to look for / find work in order to receive benefits ?

There isn't anything the op can do because her mother is perfectly happy with the moocher mooching off her. She knows op unhappy about it but is allowing this scrounger full access to her house and unlimited pocket money. I suspect mother likes the attention, drama and moaning about it. This is your mum's fault for encouraging him, I suspect if you had a frank conversation with him he will say your mum has made promises, no point tip toeing around her or him, they are both happy with the status quo. Find out exactly where you stand and act accordingly.

I’m sure she does - does she have any training?

Surely a bespoke door has a lock?

This!

OP, you really need to report the missing key. It's obvious he's playing the 'long game' and isn't going to give up easily.

The local council adult services should have a safeguarding department. They may be able to help with advice.

I'm so sorry OP, it must be so stressful dealing with such a parasite. Your DM is her own worst enemy here, it's hard to help people who won't be helped.

I would focussing on getting his stuff out for a start. I might also think about consulting a solicitor to draw up some clear legal agreement. Do you think your DM would go for that?

I have read all the OP’s posts and I am probably repeating everyone else here but your hair should be on fucking fire at this point.

You can not control this man and you absolutely do not seem to be able to predict and counter the danger he poses to your mother. As everyone has said you are very naive—in the sense that you don’t grasp how dangerous this predatory man could get. Stop thinking of him as “the mooch h” or the loser/lost boy. He is a grown man with a seedy history of use and abuse. He is proud, greedy, and shamelessly manipulative. He is potentially very, very, dangerous to your mother. Don’t be under any illusions that he can’t or won’t hurt her to gain control of her and the house.

Change the lock. Offer to move all his stuff to storage and then do it. Tell him outright that you are contacting elder services and putting then on notice that you believe he is scamming your elderly mother—which he is!

The safest thing to do is push him far, far away from your mother. Use rage, humiliation, or outright threats but do it fast. Because this man is like water. He will keep creeping into your mother’s life and rotting it from the indife. He must be stopped.

Yeah, I'd get the locks changed (sounds expensive I know, but worth it I think) regardless of whether he has it or not. It's a security risk either way and the perfect excuse to have security cameras installed as well.

At this stage, could you set up some cameras inside the home so you could monitor his behaviour and tell neither of them that you're doing this (like a nanny-cam set up) because you're not sure he's not actually taking liberties and getting his feet well and truly under the table.

Would your mother kick him out if she was presented with evidence (rather than speculation) that he has a key that he shouldn't have? If he has his own belongings still in the garage, I'd start there by saying as your mother is getting older, you need to keep the clutter to an absolute minimum so if he is storing stuff in her house, he needs to start using a storage unit and you will be checking on the progress of him getting his stuff out of the house/garage the next time you're there.

Your mum thinks that she is being kind to him but she really isn't. He might as well have a disguise on and be taking part in a highway robbery because he's no better than Dick Turpin!

I like the suggestion that as the 'spare' key can't be found, that you will have to get another replacement lock and you will take charge of the new 'spare' key so that it can't go "missing". If it's one of the coded keys (so they are much more expensive to copy than a Yale key for example) might it be possible to request notification if copies are requested from the few locksmiths that are permitted to copy them?

I hope you have notified the insurance company that the spare master key is missing.
Honestly I would step back and let them get on with it, she chooses to have him stay. I understand you are looking out for your mum but it is becoming a him or you situation, she has chosen him. I think she is being very disingenuous, there is nothing you can do about it. He knows you are not going to move in to be your mum's carer/companion. This will eat away at you.