Hi,
I'm very late to this thread so obviously no help to the original poster! However just in case anybody else comes up with this problem in the future..
HMRC state that is is your responsibility to ensure your tax return is completed, even if you have employed an accountant to do so. As such, the first thing to do is:
1) Call HMRC and tell them of the situation.
2) Is your accountant part of a body? If they're Scottish, they'll either be ACCA or ICAS. Contact the relevant body and tell them of the situation.
3) Tell your accountant you have done the above and he'll probably get his act together!
If the tax return is late, you will most likely receive a penalty so there's no point beating around the bush, get on the phone to HMRC and tell them what's going on.
A useful thing to do (even if you have an accountant) is to write down the dates of when everything is due (tax return, VAT returns if applicable, accounts etc) Maybe put them in your outlook diary or something like that. If you don't know the dates, just ask your accountant to write them all down for you. As good as some accountants are, it is really useful to be aware of all these dates as essentially it is our responsibility as business owners to ensure these deadlines are met.