One company that I was initilaly looking at was click here however seem to be expensive for some.
Also have a look click here for advice.
Upon advice, I chose an accountant that I had met through my previouse employment and have recommnended him to many people, all of them very very happy with him.
I personally am a Sole Trader and all my accounts and end of year SA, etc are done through the accountant and I just give him all the paperwork as and when he requires and he does the rest. I know for a fact that he has a few IT contractors for whom he deals with all the admin/accounting stuff. He is based in Edgware, Middlesex, but his clients are all over the country.
Send me a message through the yellow envelope if you need the accountants details and may be worth your while speaking with him.
I have always received very prompt service and advice ( almost all free! ) whenever I have needed and he has also saved me some £££