From the BBC: Archaeologists have uncovered a World War I trench system in a Scottish city park. The trenches, used to train recruits of the Argyll and Sutherland Highlanders, were found in Stirling's Kings Park after a tip-off from a retired park keeper. About 20m (66ft) of the zig-zag trench system was opened up over three days. The trenches have now been back-filled but could be the subject of further research in the future. Lorna Main, archaeology officer with Stirling Council, said there were not many training trench systems recorded She added: "It was really quite unusual to get the opportunity to explore something from that period." A similar set of trenches were discovered in Ross-shire in 2008. BBC News - WWI trenches found in Stirling park Tom.
Similarly there is a trench system in Manchesters Heaton Park where it was a training camp for the Manchester Regiment wWW1, now filled in but probably still intact under the soil , try on google earth to see if any marks are visible .