Expatriated now have to complete final tax return - stupid question!

What is so complicated that it costs £2,500? Are you subject to the exit tax? Did you have any PFICs or 5471s to file?

The OP said quite early on that they were not covered.

Many firms quote in the region of £1500 + to file returns for relatively straight forward financial affairs. especially from one of the bigger accountancy firms.

I found it relatively easy to do myself with my past returns as a guide. I filed months ago and called them last week and they confirmed, received and processed.
One just needs to take care with the form 1040NR. and my situation was not just a wage either so it is possible to successfully file the last return yourself.

and remember the final return has no relevance whatsoever on whether or not you will be covered. there are only three ways to be covered, no more or no less.
the worse that can happen is getting a fine for a late form 8854 and even that doesn't necessarily have to happen if you can prove you sent it.

One has very little to worry about once they renounce if they don't have US assets.

also when i say take care with the form 1040NR, i simply mean one is filing dual status so the form 1040NR is a new form that one would not have a past model for.

Please note that it is rare to file a Form 1040 for a year of expatriation. It is common to file a 1040 Statement; but the statement is not the return for a dual status tax year.  It is simply a statement of income and other items for the period of US residence.  It will therefore appear different in some respects from a 1040 for a full year of US citizenship.

yes this is true
mine was 1040 statement and 1040NR return, clearly marked dual status return on the 1040NR and dual status statement on the 1040 statement
if one has no US source income after renouncing, it's more straight forward to do. all the form 1040NR is treated as the main return.