You may not want to do it yourself if you have any of the following situations:
Recent move to UK on short-term contract (3 yrs or less anticipated stay) and still on US payroll.
Been here at least a year and brought money into the UK from outside the UK.
Assuming you are US citizen and UK resident, you are probably US domiciled. You should seek expert advice regarding your domicile status, as having a UK domicile has a negative impact on your UK taxes.
1) Do it online at
http://www.glueserv.com/COI/IRV1649/ - easy peasy as the Brits say.
2) If all you have is a P60, a bit of bank interest, and you are not a higher rate tax payer, you don't need to file in the UK (except if you had the wrong PAYE code and they owe you money).
3) The UK tax year is Apr 6 - Apr 5, so the return for year end Apr 5 2005 is due 31 January 2006.
4) If you owe massive wodges of dough (i.e., >£1,000) to the UK government, pay it and file 31 December 2005 instead. It will give you some flexibility for creative tax work on your US tax returns.
I should talk. I still haven't done mine yet! I'm like the dentist with bad teeth and the doctor that smokes; too busy to sort my own out.