You have a business that happens to be owned by you and you are selling it to another person (your new company). That is a capital transfer like selling shares or property, and normally would attract Capital Gains Tax.
However there is something called "Incorporation Relief" that allows you to defer the CGT charge until you finally sell the shares. To get that relief you have to transfer all the assets of the business to the new company in exchange for shares.
The book entries for it are a bit involved in the new company and you'll have to make sure you get the process correctly - including filling in your self assessment correctly once you have transferred the business.
There are a couple of other ways of transferring the business that may be better tax wise in the coming years. An overview here: https://www.taxinsider.co.uk/incorporation-relief-and-direct...
HTH