Hypothetical question - ensuring tenants leave

[MrShed]

Another hypothetical question for you all. I had the idea of a way perhaps to encourage tenants to move out voluntarily by the end of the notice period of S21, rather than having to evict. At the start of the tenancy, negotiate a seperate agreement, seperate from the AST, and take a form of deposit(perhaps a month or month and a half rent). This deposit seperate from any damage deposit, this should still be taken. Make an agreement that should the tenant refuse to leave after a valid notice period has elapsed, they shall forfeit this deposit.

Is this possible? I do realise that it would not have a widespread use, as not all that many tenants would be willing to do it. But would it be legal, and legally enforceable?

[MrWoof]

Many tenants have trouble finding the deposit, asking them to more than double it is likely to cause voids.

[MrShed]

Yes Woofy I understand that, hence saying its use could not be widespread. But would it be legally binding?