LONDON (Reuters) - Britain's biggest watch retailer Watches of Switzerland Group said on Thursday it was considering an initial public offering in London, as it looks to make acquisitions and reduce debt.The company, which sells brands such as Rolex, Richemont's Cartier and Swatch Group's Omega, is looking to trade on the main market of the London Stock Exchange, using its premium listing segment, and sell 25 percent of new and existing shares.A premium listing meets more stringent rules than..