Although rodenticides can be bought in various stores throughout the UK, the chemicals used are at low doses and often have little to no effect on the rodents that are being treated. When using rodenticides, they need to be closely monitored to ensure enough is taken to ensure the lethal dose is taken.
These baits should not be left in the open for non target species to have access to and should be in suitable containers. We advice it is best to avoid using these treatments yourself and to call out a professional to administer rodenticides. The UK is experiencing resistance in Rats to certain active ingredients, many are the ones found on shop shelves.
These active ingredients have been found in wild animals and birds and this is due to them being second generation poisons. This means that if the animal that has eaten the poison is eaten by something else, it can poison that animal too.
We as professionals are trained to use the correct thing in the safest way whilst taking into account the environmental impact and to minimise risk to other animals, wild and domestic as well as the general public. 

IMPORANT - GLUE BOARDS FOR RATS AND MICE
Glue board use now requires a licence, under the Glue Traps Offences Act 2022.
Using glue boards without a licence is illegal. Licences for use are available from Natural England.

Open traps should not be left outside due to the risk or catching non-target species such as Hedgehogs and garden birds. 
All wild birds, their nests and eggs are protected by law Under the Wildlife and Countryside Act 1981

Humaine trapping is covered by Humane Trapping Standards Regulations 2019 and Wild Mammels protection Act 1996. Welfare of animals in traps is paramount in these situtions and please be aware that mammels such as Brown Rats (Rattus Novicus) and Grey Squirrels that are caught in humaine traps do need to be dispatched according to law. You can find more information here