The audacity of my tenant has left me bewildered!

As they entered with the consent of the previous tenant they're not squatters. So the trespass route is out, yes I'd wait two weeks and then s21 9
Or S8 as appropriate

FirstlyI personally would report he malicious vandalism to you property to the police - if the police say it is is a civil matter and say they won't get involved - then I would remind them that malicious vandalism is a crime and you are reporting a crime - and would like a crime number !

Secondly in addition to your section 23 notice I would also issue a parallel section 8 citing all the breaches to the tenancy agreement - including rent arrears, damage to the property, illegal subletting etc.

You should be ready to ask the court for a possession order the day your notice expires - and apply for bailiffs they day you get that notice.

You may wish to advise your tenants you are doing this and that if they don't want a CCJ against their names that will harm their ability to get another home - from either private Landlord or the council they should be out by the set date!

If you don''t know what to do I suggest you get a solicitor or specialist eviction agency on the job ASAP

I ALWAYS issue a claim so the tenant gets a CCJ. If you have no prospect of ever getting renta arrears paid or compensation then just issue the claim for £300 as this will only cost you £35.00, and believe me, it does stuff them for another 6 years.

Also issue a common law Notice to Quit. If the tenant is no longer living in the property then it will not be an assured tenancy and you may be able to recover possession more readily. You should consult a housing specialist solicitor to check your options.

Reply to the comment left by GlanACC at 16/10/2023 - 11:40
And after five and three quarter years you can issue another claim for the remainder of the debt at their last known address. that screws them for 12 years.

Unless you are confident that the Surrender document is worded substantially as being a written notice given by the tenants, then it may not be worth the paper it's written on (although to be clear, I'm not an expert).
A Surrender of a tenancy is usually enacted as a Deed which means their signatures should be witnessed by an impartial 3rd party. It also should be done voluntarily by the tenant and not under any duress. I'm not suggesting you put pressure on them at all, but putting it in context with the S21 and the property damage, it may be seen in that light, especially if the tenant goes to Shelter for representation.
Written notice to end the tenancy, is what you should have gotten from them. That would have ended the tenancy for certain regardless of whether they left or not.
I've never had to pursue a tenant who didn't leave after giving notice, but the tenancy would be at an end, so presumably you have more power at that point.
It sounds as though you may need the advice of an expert as to how best to proceed. At least you'll know if there are any faster options open to you or not. I hope they leave for you and you don't need to do anything further.
As far as your options regarding the damage; the police won't do a thing, because there's no evidence of who caused the damage. You may get a crime number for your insurers if they require one, but that is it! Your tenant is only liable contractually, not criminally for the damage caused, unless you have cast iron, irrefutable proof, (video, or impartial eye witness type proof) that they deliberately and maliciously caused the damage.

Reply to the comment left by David Houghton at 16/10/2023 - 11:19
The poster is talking about the original tenants not the sub lettees

There is some good advice here for you. Damage and other stuff aside, Don't spend too much money on Solicitors until you have to because most of what I am going to tell you is not difficult to do yourself. I have a tenant who will not leave. I just did the legal route, notice to quit, court application to get an official judge's Order (he was given 28 days to move out). He is still there so I filed an N325 (bailiffs) this week and eventually, the bailiffs will come and march him out of the door. At that stage, if the tenants have left any belonging behind, you give them a time limit, in writing, telling them they have a certain time to remove these items and if they don't you will remove and destroy them. Of the latter, it may not be strictly right, BUT I doubt that anyone will sue you for it. I've nearly had a nervous breakdown over this, trying to be fair has got me nowhere, but 'mostly' we have to stick to the law. I hope some of what I have said helps.

Reply to the comment left by Marie Lee at 21/10/2023 - 08:20
Yes you are right. On the latter, you need to be able to determine the items are abandoned. Two weeks notice doesn't strictly determine abandonment, but is evidence of it.