wa alaykum salam wa rahmatullah,
Welcome to the UK brother. We should shop from anyone, and it is good to give preference to the Muslims. We should do our best to give our love, cooperation and support to every Muslim, and not be seeking out whether they are "Salafi" or not. There is nothing in our Deen, nor from any of the ulema which states a person does that. Most Muslims run honest and good business operations, halal meat is halal etc - We should do our best to maintain good, friendly ties in our community unless there are specific valid reasons not to.
You can find further support from the mosques in Luton. Do you know the address of good masajid? I recommend Luton Islamic Centre:
Luton Islamic Centre
116 Bury Park Road
Luton
Bedfordshire
LU1 1HE
UK