You will get in trouble for the rats as they have protection under animal welfare act, (if there were a cat in the house you could be done for harrassing either species!) and as most tame species of R. Norvegicus are “pretty” colours its blatantly obvious they aren’t wild ones.
This does not apply to filth flies, but unlike mammals with a known gestation period the development period of larvae varies with temperature (hence why you see more in high summer).
I found this out as I had to deal with a infestation of filth flies in a wheeled bin last time we had a decent summer (years ago it seems) also there was a family of rats in my old office and I was going to live trap them (as they were smart enough to hide when I let in a random cat, but made a racket above my head when it was bad weather and the cat wasn’t around.
There was all manner of rules about this (the traps weren’t cheap either) and we moved to a new rodent-free office anyway. I was going to take the rats to Stowmarket (where they would be let free by the river).
I still have a public service issue clipboard I got from my old work (environment ministry), and was wholly tempted if I encountered any locals to say “I’m working as a contractor for Mid Suffolk District Council and Defra – under the EU Winter Mammals Directive 04/2879 these rats are being transported to your area to ensure there are enough to see you through the winter, as we are obliged by EU law to ensure you have sufficient in your neighbourhood. You may have already heard on the news people in London saying “you are never more than 3 metres from a rat” – and getting them to actually sign for the rats!
