We don’t think you need to worry too much about if legislation prohibits moving because legislation always overrules contract.

The problem with trying to alter the start date to an unknown date (on something occurring) is does the end date also change? Ideally you want a minimum six months from whatever start date for council tax purposes. (If you’re doing a 12 month fixed term there’s less of a worry).

We think one way might be to simply adjust the rent rather than the term.

The other piece of advice we would give is you should say it as you see it in simple terms. You can mutually agree any additional clause freely and a negotiated special clause like this won’t generally be governed by the Consumer Rights Act (in any event it sounds to be beneficial to the tenant and not you).

Here’s a similar clause we created for a commercial lease granted in April last year just when we were in the thick of the first wave. It was for a hairdressers so there were clear and real possibilities of prohibitions for its use. Perhaps you can modify that for your needs. Any clause you create can either be put in the additional terms in the Builder or simply by way of separate agreement (e.g. by email):

The tenant paying the landlord rent at the rate at the following rates on the following dates in advance:

22 May 2020 to 31 May 2020, zero
01 June 2020 to 30 June 2020, zero
01 July 2020 to 31 July 2020, £xxx

And thereafter, if ‘hair salon’ remains prohibited from opening by official government guidance and The Health Protection (Coronavirus, Restrictions) (England) Regulations 2020 (or other replacement regulations), at a rate of £xxx per calendar month payable in advance on the first day of every month. Otherwise, when ‘hair salon’ is allowed to open (even with restrictions), at a rate of £xxx per calendar month payable in advance on the first day of every month. For the avoidance of doubt, if ‘hair salon’ is allowed to open between the second day and last day of any month, only the £xxx will be payable and the £xxx rate will become payable the following first day of the month. For example, if hair salon is allowed to open on the 4 July 2020, £xxx will be payable 1 July and £xxx will be payable on 1 August 2020 and thereafter.