Tesco Mobile is run by the supermarket of the same name. Just like the supermarket, it aims to offer very low prices. It is a budget virtual mobile network that is one of the biggest in the UK. In fact, as of June 2012 it had over 3 million customers. It runs on O2 and is actually part owned by this network too. Initially it was easily one of the cheapest mobile networks available and offered superb customer service. However, it is now possible to save more money with some of the other budget networks.
Since the network runs on O2 the coverage is exactly the same. It should be decent wherever you are and very good for 3G in cities but to be sure we would recommend you check out the coverage map for your area to see the exact situation where you live and work.