Gerry Doherty, leader of the TSSA transport union, said: "Our members will be striking on Friday to defend the full service they give passengers, including advice on the cheapest ticket option." On fares, he said: "Passengers are facing a double increase because the company is placing further restrictions on cheaper off-peak travel. Those who wish to make a day trip into London before 11.30 am will now have to buy more expensive fares."