Pests in hot weather?

Who on earth commissioned a 300 job to remove a harmless pest! A couple of pots of ant killer from poundland would suffice. I could justify the bill if a swarm of bees had been involved even a wasp nest but this way over the top for ants.

If they asked you to destroy the ants they should pay. Usually 'flying ant day' is one day a year, so I don't know if £300 is excessive for a pest that was going to die naturally.

Don't ask Mary Poppins.

£300 is outrageous. If the tenant can't deal with a little problem like ants and they asked you to deal with it then it is their bill not yours.

ha ha, I bet they were battling all day trying to beat thousands of never ending flying ants, if your tenants thought they are entitled to call pest control to deal with a problem caused by once a year occurrence of flying ants, in my view they would be the first you need to get rid of otherwise you will face the same problem over and over and over again the minute they see the first flying ant.

I’ve had this a few times in my own house. I just spray them using a can of fly spray costs around £2.
As you have a clause in your AST then the tenant has to pay. However regardless of such a clause it is still the tenant’s responsibility. It was established in Warren v Keen 1953 where Lord Denning said that a tenant must look after the property in “a tenant like manner” doing all the little jobs that a tenant is expected to do. This would include for example changing light bulbs, changing a washer on a tap, clearing a blocked toilet and sorting out insect infestation. So this is a matter that should have been taken care of by your tenant.
(Having said that I’ve had a few instances of wasp nests in a couple of my properties and because my tenants are really good, pay me on time and never any hassle, I agreed to arrange for a local pest control company to sort the nests out). A bill I paid earlier this year was £70 so £300 is way over the top here. It’s your tenants bill to pay.

The only reason a landlord would be liable to pay for pest treatment when you have a clause such as yours is when the infestation was already present when the tenant moved in, (eg the carpet was full of fleas which all hatched out when the new hosts arrived), or if a defect in the property caused the infestation to occur, (such as a drainage problem, or cavities allowing rats to gain access).

As others have said £300 is ludicrous for flying ant treatment. Did they ask you to agree to them getting the pest treatment done before hand? Did you approve it? Did you or they get a quote first?

Even for work that is something you would normally pay for most tenancy agreements warn tenant's not to have work done themselves without first getting approval to do so or they are not guaranteed you will meet the cost. If you did agree to the job being done and didn't ask the price first you may be in something of a moral conundrum. In that case I would get a couple of quotes for a comparable service and offer to pay that amount only and either you or they should challenge the price and try and get a significant reduction from the pest controller.

If they've simply engaged the pest controller without any approval from you, then I would just direct them to the relevant clause in their tenancy agreement. They'll certainly think twice the next time they try dipping into your pockets as though money's no object.