Trying to sell

Slithery

I'm not quite sure that you understand the situation that you are in...
No-one is going to be buying or even interested in your property until after the tenants have left, leaving you with two options.

• The legal route - You say that an S21 has been served, are you sure that it's valid? After the 6 months is up the tenants still don't have to leave if they don't want to, expiry of the S21 just means that you are now allowed to start court proceedings to evict the tenants from their home. Seeing as how the courts have been closed for months and there is a mahoosive backlog then legally evicting your tenants may well not happen until 2022.
• Mutual surrender - Offer your tenants a financial incentive to leave ASAP so you can start marketing the property. I'd suggest at least a few months rent as an opening offer but be prepared to have to go higher.

NameUnavailable

There's a number of issues here;

You've just given them 6 months notice so they don't need to leave until next April/May at the earliest, assuming the tenants co-operate, but they can decide to stay longer.

We are about to enter lockdown for a month. Given the increasing rate of infections it's perfectly reasonable for them to refuse access at present (and I would say rather sensible for them to do so).

Most buyers will be advised by their solicitors not to exchange contracts on a tenanted property so you are not going to sell before the stamp duty holiday (unless the tenants decide to leave early).

The above assumes we will be back to pre lockdown state of play again next spring. Who knows?!

I would not be pestering tenants right now especially given that they still have at least 6 months in the property.

Your options are to see if they co-operate (after this lockdown period), OR wait until they have left OR offer them a financial incentive to vacate early.