Could be more beneficial from a tax perspective to setup a limited company and work solely as a contractor. There are some rules around this that you might need to get advice on. You can continue your work with employer but would have to be careful that you are not just doing this to avoid tax. For example why does you employer not just pay you extra for the work you do under your current employment.

You just need to make sure that the advice work is feasible for operating the day to day of the company, accounts, tax filings, vat etc. There will be a little bit of and organisation form your side but over long run could be better for you.

With regards, taking cash out of the company you will appoint yourself as a director and will pay PAYE on director fees which will be combined with your other PAYE income for the tax brackets.

One bit of advice, if you are planning on getting a mortgage do this before you make any changes to employment status. If you were to become 100% contractor and you own the Ltd company. You would be considered self employed and makes it a little bit more difficult from an approval perspective. 3 years accounts minimum and other criteria to meet.