To never do them a favour again?

I get why people think you need to explain /defend yourself but I would not; neither would I complete the work but perhaps you are nice than I am.
Is your Mil usually such a thoughtless arse?
Just "I am sorry what I could offer you at no charge didn't suit you, here is your paperwork back. Please feel free to look elsewhere.

You could just hand the documents back, given your illness and the newly advised deadline, and let him pay someone else to do the necessary.

It's amazing how.people seems so ready to complain if you are working for free ias a.favour,.instead of speaking to you properly and actually offering to take the papers back.whem they realised you'd been ill.

Nobody values stuff they get free and if you do this service as a paid service usually then you aren't valuing yourself by doing it free
You are basically handing your in Laws however much you could make doing this for paid clients, possibly hundreds of pounds - maybe think about that before you offer freebies

“I’m prioritising my paying clients. Feel free to go elsewhere.”

He can fuck right off and for goodness sake don’t be a mug like this again.

That's awful. Reminds me of a recent thread where someone's mum told her friend that she only had to pay a tenner for the OP's professional services, after her spending quite some time on something, and people were saying she should accept it. You don't see men's time and expertise being devalued in this way.

Some great responses! Please stand up for yourself!

This is the right approach.

I would say you're really ill and won't be able to get it done by his deadline so he should get someone else do it.

People like this only learn if you speak their language.

And don’t do any offers for MIL again

Get DH to tell MIL to never offer your services out like that again.

“Terribly sorry BIL, I was unaware you had a deadline. With me being unwell and being flat out with actual clients, I don’t have capacity at present to meet your required timeline. I’ll drop your paperwork off* so you can get someone else to sort this for you”

*or make him pick it up, or have DH drop it it to him

Today I’ve had a message from the partner asking where the completed work is as he has an important deadline in a couple of weeks (not mentioned before and not something I’d have been aware of).

Tell him he needs to find someone else as you were unaware of this deadline, and if you had known about it you would not have offered. Apologies and all that.

Next time don't do favours, especially ones volunteered by MIL.

I’d send the paperwork back and tell him he can shove it up his arse!

It's not ideal though. When I do work for free I still expect to meet quality/timescales.

Just set your own new deadline and meet that. No need for them or you to get uppity, it just creates resentment.

This sounds ideal.

Do the minimum necessary to get it back to him, and never do it again.

I wouldn’t be bloody doing it at all after that, ‘I’m still recovering and as X needs it by this date I’m unable to help him, here’s a contact for someone who can’

Hi sil partner, i wasn't aware of this deadline and would not have agreed to it. I have been off work sick so other things are now behind schedule. Obviously I will be prioritising paying clients over a free favour I was volunteered for. I was planning on doing it this in my personal time but have since received another message about this fron MIL saying it needs to be done immediately. I'm now pretty annoyed about all this as I'm sure you can understand. You will have to get it completed elsewhere. I will return your paperwork whej I'm back in the office later and recommend you try X."

I'd say, as you've been unwell, and the work is now urgent, they'd better give it to someone else.

It really is no good deed unpunished. And as any solicitor will tell you even free advice kindly given if wrong means the buggers can sue you!

I wouldn't do it at all now.

Yes to this! They are taking the piss. If urgent then you pay.

@Pipiscoming2023 I would send sils dp a mail and copy to mil saying that you were never told about a deadline. If you had known you wouldn't have accepted to do it since you got paying clients that take priority. They all know that you have been ill and you are now back to work. Since there is a rush you won't be able to help out and you will send him back the paperwork so that he can pay someone to do it. CF!!

I know, I hate it when other people are free and easy with your time and money offering out favours to make themselves look good.

I once got dropped in it like this when I had done a small favour for another family member. "Oh Gingercat will do this for you ...."

My sister volunteered me to do something else. I told her I have done my voluntary work for this year so you will have to re-apply next year! It did not go down well but I have not been approached since.

I would send the paperwork back with a very sharp message and let him run around and find his own slave to do free work.

I’d be having a word with your MIL , how dare she volunteer your services for free.