Rats!! Advice please

The rats will be living in the attic because its warm, dry (even with the latest level of loft insulation, it'll be a lot warmer and drier than outside), and safe.

First, the rats need to take the poison before it takes effect. If they're evading eating the poison, they have a good safe food source, then it won't have any effect.

Rats are very nifty travellers, shinning up drainpipes, chimney breasts, up walls and adept at travelling for good food sources. Dustbins, wheelie bins, composters, street food (discarded take-aways), the list of possibilities are endless in the urban world.

For the rat poison to take effect, the entry and exit points will need to be identified, and blocked. Blocking an entry/exit point is only the start, because they will find alternative entry/exit points.

Before blocking any entry/exit point(s), ensure that no building regulations are being infringed, every property will have vents to conform to build regulations at the time of build, and/or improvements/alterations undertaken after the property was initially built.

We have a formidable amount of rats in our chalk quarry, fortunately none inside dwellings! The 'ratman' came & supplied poison to be put under properties but the rats do not eat it ... I have had to stop feeding birds and hedgehogs, even give up my goldfish pond because the rats were swimming to take the fish food ... most folk are now using either humane or lethal traps with some success! I sympathise with you having them in your attic, are you able to set traps to catch/ kill them?

pestologyltd.co.uk/.../
Also Rats as well as damage inside buildings and lots of health risks as wekl. Rats can and will naw through electric cables of which can cause fires. There are lots of Rats can get in to a building even if everything is blocked off at ground level. See link above!