In case you don't want to pay an accountant, or want to know your options, this is from memory a list of the things I first had to do:
- Register a company with Companies House, this is very straightforward and quick
- Register on the HMRC website, then
- Register your company for VAT, and
- Get the HMRC software for calculating PAYE
- Register yourself as an employee (filling out the new employers part of your P45 from your old employer)
- get a bank account. This took the longest, if I had got a overdraft and/or CC it would probably have been even worse.
- a company has to have initial share capital (£1 per shareholder is enough) so you have to pay this into the account when it's open.
There are lots of HMRC guides on various aspects, most of them quite readable, eg 'all the things you have to do before paying someone for the first time'. Sounds like you will be covered by IR35 (tax rules for people working for one company through their own companies, where their situation is similar to an employee) so you should find out about that.
Start keeping records of any expenses. Keep receipts for everything - it will be advantageous to pay 'yourself' back from your company when it has made some money. Keep all the letters you get and find some way of dealing with the various passwords, PIN numbers and logins. You need to keep various records such as your P45s. You will need to make payslips for yourself as well as VAT invoices for your client. Find some accountancy software or start out with Excel. You can get an accountant to cast an eye over your accounts at a later date, without paying them to set up the company.
PAYE has to be paid by the 22nd of the next month, and VAT has to be paid by the start of the month after, eg if you receive a payment from your customer in May you have to pay the VAT on it by about July 7th, if you pay yourself a salary in May you have to pay the tax and National insurance by 22nd June. Put the money aside as soon as you know how much it is.
If your turnover is quite small you can apply to pay VAT quarterly instead of monthly. You should also apply for fixed rate VAT, which will save you money if most of your company's income gets paid to you as wages or dividends, and also slightly reduces the paperwork.
Please someone say if I have forgotten anything crucial!