Help – tenant’s friends moving in?

There really isn't much you can do. Other than tell them you're unhappy and serve s21. The accelerated process is just admin and you should not need to go to court or pay a solicitor

Are you in a Selective Licence Area?
There could be a breach.
Does it breach the AST.
Get a waiver of rights signed by the non tenants.
Serve notice immediately to minimise any losses.

I must stress I am not an expert but I was asked about a similar situation a while ago and did some research. I don't know anything about the overcrowding issue that was flagged up. My research, and I can't guarantee it is correct, was:
1. You could either choose to add the additional occupants to the AST. In this case, they would be joint tenants with the original tenant.
2. Or there is such a thing as a contract for a named "permitted occupier". This means that they are allowed to use the address, eg officially, but that the original tenant takes full responsibility for them, eg that they will move out when the original tenant does.

Hope this is helpful but I don't think you should just "hope".

Reply to the comment left by Alexa Dalbya at 12/04/2023 - 12:04
Our tenancy Agreements state that only the named people can live there. Any changes require an amended contract. If there are extra people, we charge more to cover the extra wear, gas, electricity, etc, included in our rents. The tenants have always kept to their agreements. It would be immoral not to,

Two considerations
1) It may not be relevant based on the limited information as to the EXACT detail of who would be in the property but you might want to be aware of Statutory overcrowding legislation and mixed gender accomodation.
2) "The tenants have indicated that they are likely to go (tenancy ends in 6 months’ time) but my concern is that the friends might not."
Your agent appears to be rather complascent, It may not be neccessary or even desirable to enter accelerated procedures for possession but it might be advisable to have them write to the tenant specifiying that, presumably, although the AST does not prohibit GUESTS (it can't), it DOES prohibit any subletting and also that there are no "Permitted Occupiers" on the tenancy agreement and that neither has a request for that been received. The agent can, so far as I am aware, make a charge to the TENANT for adding the Permitted Occupiers who have no rights to the property and the agent must carry our Right to Rent checks even though the P.O.s aren't actually renting, your tenant should be told that they remain 100% liable for all rent and other costs if their "guest" does not leave. Put it on record rather than leave it to chance.

However genuine your tenant sounds far too often their generosity is at your expense. Whenever I've discovered an unauthorised occupant there's been substantially more work to wear and damage to refurbish after they leave.
'Friend' may be a convenient description - if the friend is paying any amount they are sub-letting and your tenant must comply with all legislation.
I'd move quickly to use whatever grounds you have available - AST, mortgage terms, query if sub-let - to notify the tenant formally that they you don't accept the situation. If you set the rent for a single family of 2 or 3, serve notice of a rent increase if you can - e.g. for the extra wear and tear, and (now) 4 occupants.
If the 'friend' does move in, don't hesitate to begin action to remove.

1. If your tenant contacted your agent first to tell them this, then your agent should have straight away stated that this will more than likely be in breach of the AST and advised accordingly that this wopudl be unacceptable. (If your agent did the AST check it NOW to find the suitable sections)
2. you dont say if current tenant is still within the first 6 months of the AST. If so then you cant serve notice yet. (NB also makes me smell a rat - did the tenant get the AST knowing that they were going to move the 'friend plus 1 in asap thereafter?)
3. do a LL check asap. Write to the tenant stating they are in breach of the AST and that you will be coming over at X date to discuss this further.

Reply to the comment left by DSR at 12/04/2023 - 13:15
Sounds very suspect. I would meet the tenant and the 'friends' ASAP and get agreement to additional rent, check that they aren't subletting, get written commitment the tenant is responsible for the friends and will ensure they leave when they do. In short, as much cover as you can get. If they don't want to comply, they will probably be in breach of their AST, and you can serve a S21 after the term.

As Bean rightly says this could create a serious issues if you are in a selective license area. If so 1) serve s21 noticea asap before they move in. 2) contact your local council advise them of the situation and it is without your consent and ask for a temporary exemption from licensing. If they refuse then take that to a first tier tribunal, by the time that comes about you will probably have possession anyway. If not the tribunal will probably go your way and don't forget to ask for your costs from the council

As wel as my license questions,
You will have a HMO if they move in.
Does it comply with the additional regulations?
And,
Are you in an Article 4 zone which would mean you need planning permission too?