Tower Investigations Ltd was set up in 1997 as Tower Debt Recovery Ltd, changing its name in 2004. It appears to work closely with Global Debt Recovery Ltd although they don't share the same registered address (as often happens when there's really a single company operating under different names). Global Debt Recovery Ltd was originally known as Tracing Associates Ltd and its website makes it clear that they still work in the same field:
http://www.globaldebtrecovery.com/services.htm
Basically it seems that one of those companies is chasing up old debts from information supplied to them by the financial industry (such as a credit card company). You can probably simply ignore it but it might be worth taking out a free trial (and then cancelling it before any payment is due) with Experian to see if there's anything listed on your credit file that you don't know about.