As long as they are E marked then they are suitable for sale and use in the UK. I see no problems. Are you staying to a size that the manufacturer fits as standard??
Ihave fitted BF AT's to my Disco (see avatar) and also changed the size (from 255/65/16 to 245/70/16's) and did check with my insurer, and was catagoricaly told that it was fine, and had no bearing.
Maybe if you changed to some oversized mud pluggers it may have an impact, but knowing that insurance companies use every trick in the book to get out of paying up in the event of a claim