To never do them a favour again?

This covers everything and is assertive without being overly defensive or arsy.

Nothing given for free is ever appreciated.

YABU. You should not have said you'd do it free of charge. You were leaving yourself wide open for 'No good deed goes unpunished',
Having said you'd do it, you were ill, which could not be helped, but you should have kept the BIL informed of progress.

I don't understand why your MIL got involved but I've not RTFT.
Stick to professional arrangements where work is involved.

I've done something similar, and being shouted at by a CF is no fun.
My time is as valuable as anyone else's.

I agree

If you're providing a professional service, albeit unpaid, you still need to be professional about it

People can be such twats. Been in similar situations to you OP. Demanding and ungrateful friends and relatives are the bane of many a life. MIL had no right to volunteer you. SIL has a cheek to be so vocal and judgmental and BIL should be told: I was trying to do you a favour. No one mentioned deadline until X date. This situation has seemingly caused a lot of upset when I was only trying to help. Given your time sensitivities I think it would be best if you paid someone to complete on time as due to being very unwell I need to prioritise paid work this week.

Im guessing the OP is an accountant. Maybe a lawyer.

don’t give it to them at all now. only way they will learn their lesson to not be a dick.

He should have told OP there was a deadline though. OP was railroaded by MiL, so that needs to be nipped in the bud. Easily done with a flat refusal the next time she volunteers OP’s services for free.

???

If he was relying on the work then he is bound to be anxious that it hasn't been done. The point is you offered to do it. So really it does need to be done. But don't offer again.

https://27bslash6.com/p2p2.html

^this did the rounds years ago.

Well you need to read her the riot act too - a) for offering your services and b) for chasing you when no deadline was given and you were ill!

Dont let her get away with it OP. Tell her you won’t be doing FIL’s anymore either as you are very upset.

No favour goes unpunished

This - speaking from experience!

I think the fact it’s free work is a red herring (though it obviously rubs salt in the wound!). If you agree to do anything you should do it properly no matter paid/free. Key here is that you didn’t agree, your MIL volunteered you, so you didn’t get to go through the usual convo about timescale etc. I would just tell him the date you can do it by, and suggest he goes elsewhere if that doesn’t suit. Also politely advise everyone in your family you can’t generally take this sort of thing on but if you do then it can’t be taken on unless specifically requested to you direct.

Dear massive CF.

You’re aware that l’ve been ill and haven’t yet managed to get around to the freebie for which l was volunteered. My illness has caused a backlog which has to take priority because it’s scheduled, paid work. Since l wasn’t made aware that there was a deadline for your own work, and since l am unable to meet that deadline you have a couple of options. I can return the paperwork to you, and you can engage the services of another professional, or alternatively l estimate l can complete the work by x date. Please let me have your decision ASAP.

Dear MiL.

I would ask that in future, you would keep in mind that l provide a professional service, and not volunteer that service unpaid to friends and family. Any further offers you make on my behalf may cause you embarrassment as they will be met with a refusal.

"And absolutely do not recommend somebody to them - they will then blame you if they have any issues with that person or think their fee is too high or whatever, this is all just not your problem and nothing to do with you!"

This
-you get blamed for any costs or problems
-you've just sent a cheap whingeing arsehole to your fellow professional, might as well send them a poo in the post
-meh, let CF's fingers do the walking. I know who is good at certain things, who is busy with a long waiting list, who is cheap or expensive, who doesn't work Saturdays or lates, who has radar for CFs and won't touch them with a bargepole. If somebody is nice but just can't afford us I help as much as possible. If they are rude ( and it's not an emergency where delay would cause animal suffering) I just politely suggest they try elsewhere and they can find out themselves what's available.

Honestly for the sake of family harmony I would play dumb and say “I’m so sorry, I didn’t realise it was urgent, I’m so behind with work having been ill, of course you must have the paperwork back, I hope you get it sorted soon”. And return it asap, today if possible.

But then I’m not very assertive but there is no way in hell I would do the paperwork either.

In her first post the OP says she offered, only revealing later that MIL volunteered her, something she could have refused but didn't. So yes, she offered.

It’s amazing how grabby and impatient people can be over someone else’s time and efforts. I hope you’re telling your DH to explain to your MIL that he’s been unreasonable in offering your services for free … cheeky fucker!

Well you

Id reply and say ill have it by end of week or whenever as ive been unwell and need to focus on paying clients, but also that in future I wont be able to help out anymore because of the above. Id attached details of a few contacts id recommend too.

She didn't... She was volunteered by mother in law

Yes, it's the opportunity cost...

By doing any freebie the professional is missing out on earning money...

This needs to be MASSIVELY flagged up with whoever is receiving freebies /volunteering your time...

Yes Mil you're essentially wanting me to give this family member 1500£./x amount.... It's real money I'm losing...

They'll push back of course...

My family members would often volunteer my professional services to random peiole... Oh devils avocado will help... She won't mind... It's onyl a quick phone call... (it never was and also meant I was plunged head first into other consequential work I had to do as a result.)

Some of these people barely thanked me... For sometimes HOURS of help.. And often at madly short notice.....which would have cost them four figures. (several of these were.. Can I have. 15mins call while you're cooking supper... Which inevitably meant a.call back after supper... Then follow up mail... My one free.evening gone..

🤔

I started saying no more forcefully....after. I was burnt once too often...

Say this!