Anthony - you'd need to apply to
determine the lease and merge it back into the freehold
A few things to consider before doing so - firstly the two titles/tenures need to be in identical ownership
If the property is mortgaged you'll need to speak to your mortgage lender to get their consent and approval
There can be reasons for keeping the lease running in such cases as the lease includes rights for example that might be lost if it was determined/ended
I would always recommend getting legal advice before merging the two just to be sure and your lender (if there is one) may insist that you use a conveyancer anyway