Typically, a founder will be the (or one of the) initial subscriber(s) for shares on incorporation of a UK private limited company. These shares are usually issued at nominal value and the founder pays this aggregate nominal value in cash into the company bank account. Whilst it is possible for a company to issue shares for non-cash consideration, which in this instance could be via an assignment of intellectual property from the founder to the company, the value of the shares at incorporation is usually nominal / minimal so a cash payment is relatively straightforward.
Learn More: UK Founder Series: Setting Up Your Private Limited Company