As a qualified and practicing mortgage advisor being in prison will affect which lenders you can use but it will not stop you getting a mortgage.
Don't use an online broker for this as you need face to face advice to ensure the advisor really understands your situation. Try to find someone local to wherever you are who charges no fee, or at least charges no more than �495 which is what most reputable companies see as their limit at present.
Whatever you do DO NOT ring The Mortgage Lender (TML) or any simialr companies which you see on the tele as they usually charge HUGE fees - just look at the small print in any advert (even in Yellow Pages) as many will charge loads when you can get the same quality (or better) advice for less than �500 or even free.
If you don't want to talk to an advisor face to face for any reason try BM Solutions (www.birminghammidshires.co.uk) or GMAC (you'll have to ring them), otyherwise speak to your bank.
You will get a mortgage but just read all the fees statements VERY carefully!