After selling through a stockbroker or bank, if your shares are registered within the CREST system, these are now paperless and you would only need to complete a CREST Transfer form, which would be sent to you. The remaining shares would remain registered in your name.
Pre CREST, when shares were registered in the owners name and held in certificate form, the seller would complete a Share Transfer Form, which would be sent to the stockbroker/bank with the certificate, which they would get split by the company's registrars and subsequently return a new certificate for the remaining shares to you as the original holder.