Yes, don't worry, B&B in UK is very safe. And you get the chance to live in a family house which to me is fun to learn and experience more about British life and culture.
How about Holiday Inn? This chain hotel offers competitive prices for some locations over UK. You may make advance booking through it official website - ichotelsgroup.com
There may be special offers by other brands e.g. Le Meridien, Sheraton, etc.