Which of these is not an underground rail system in the UK?

Manchester does not have an underground rail system.

The Glasgow Subway is an underground metro line in Glasgow, Scotland. Opened on 14 December 1896, it is the third-oldest underground metro system in the world after the London Underground and the Budapest Metro. Formerly a cable railway, the Subway was later electrified, but its twin circular lines were never expanded.

Merseyrail is a train-operating company and commuter rail network in the United Kingdom, centred on Liverpool, Merseyside. Merseyrail was established in 1969, but was integrated into one system in 1977 when new tunnels were constructed under Liverpool’s city centre and Birkenhead, connecting previously separate railway routes. This created a large, comprehensive urban railway network.

The Tyne and Wear Metro, also known as the Metro, is a light rail system in North East England, serving Newcastle upon Tyne, Gateshead, South Tyneside, North Tyneside, and Sunderland. It opened in 1980, and in 2007–2008 provided 40 million public journeys on its network of nearly 78 kilometres (48 mi). The Metro is usually described as Britain’s first modern light rail system.