Not unless your written contract says so.

Some organisations have adopted 'flexi-time' systems which allow you to work a certain number of extra hours beyond your normal working day and then reclaim those hours as time off. The rules for this kind of scheme are likely to be found in a written policy, which may or may not be contractual.

Beware of building up too much unused flexi-time, as it is likely to be written off eventually under your scheme’s rules. You are unlikely to be entitled to any compensation for flexi-time accrued if your employment ends before you have used it up (for example, owing to redundancy) unless your written contract contains a written term that clearly gives you this right.