A long shot: badminton racquet left on train

If it is found at Wimbledon, by the cleaners, then it may find it's way to South West Trains lost property, which can be contacted at:

Lost Property office, Waterloo Station.
_{(take exit 2 from the main concourse or access it from Waterloo Road)}
0730 to 1900 Monday to Friday
Tel: 020 7401 7861
Online: www.southwesttrains.co.uk/lost-property-form.aspx

If it is found anywhere else, including by a driver, it should find it's way to London Underground's lost property place which can be contacted at:

TfL Lost Property Office,
200 Baker Street,
London.
NW1 5RZ
0830 to 16:00 Monday to Friday
Tel: 0845 330 9882
Online: www.tfl.gov.uk/tfl/contact/lostproperty/default.aspx

You should allow at least 24 hours before making contact (ie, give them a chance to get the item of lost property from wherever it is found to their central office) - ideally 2 or 3 days is best.