LONDON (Reuters) – Virgin Media-O2’s owners have opened talks with investors about building a new fibre network that could also be used by other smaller broadband providers, putting pressure on Britain’s market leader BT. Spain’s Telefonica and Liberty Global were holding talks with pension funds and infrastructure investors to see if they would back a new fibre network covering around 7 million homes, a person familiar with the situation said on Monday. BT’s Openreach is Britain’s leading broadband network that is used by both its retail customers and other broadband providers which use it on…