MPs and the mayor of London have added their voices to the chorus of criticism of Eurostar after it announced that bikes will have to be dismantled and boxed up for its cross-Channel trains.

Currently cyclists are charged £30 to take a complete bike on Eurostar via a registered luggage system. But from 1 November, they will have to dismantle their bike and box it up using the same service at the same price.

More than 7,300 people have written to Nicolas Petrovic, the chief executive of Eurostar, expressing their dismay at the policy. Now Boris Johnson and MPs of the all party parliamentary cycling group (APPCG) have piled on the pressure on Eurostar to reverse its new scheme.

“I am writing to Eurostar asking them not to end their simple, effective bike carriage service ‎used by thousands a year,” said Johnson. “It is a backward step, ‎which undermines Eurostar’s green pretensions.”

Ruth Cadbury, co-chair of the APPCG, said: “Eurostar, as a self-avowed champion for sustainable transport, should be looking to make cycle-rail integration easier, not more difficult. As things currently stand they’re coming across as anti-cyclist.

“Across Europe we’re seeing high-speed rail accepting complete bikes, and here of course in the UK, there is no need to box up your wheels. Eurostar is bucking the trend and stepping back to the detriment of its cycling customers.”

Eurostar said its new policy was designed to use the space on its trains more flexibly, “by carrying the same or more bikes depending on the demand from passengers”. The company added that it had to balance the needs of cyclists with those of other passengers, who increasingly want to take registered luggage.

“By changing our policy slightly we can continue to meet the needs of cyclists, whilst also helping other passengers with their registered luggage requirements,” said Eurostar.

A spokesman said the company intended to press ahead with the change. Eurostar has written to concerned passengers, telling them that “our staff are trained and ready to assist with the new procedure”. Eurostar will also provide the boxes.

Eurostar has already had to tweak the change after it was pointed out the initial dimensions for the bike box were too small. It subsequently said there would be no size limitation.

CTC, the UK’s largest cycling charity, has joined forces with cycling groups in France, Belgium, the Netherlands and Germany, to block the change. The European Cyclists’ Federation, which represents cycling bodies across Europe, described the policy as “extremely inconvenient”.

Lord Berkeley, secretary of the APPCG, said: “There are already enough inherent difficulties within the Eurostar service for those travelling with their cycle without these proposed changes making things more awkward. I can only urge Eurostar to rethink their policy and look to engage with CTC and the European Cyclists Federation to find an amicable solution for all their users.”

Sam Jones, a CTC campaigner, said: “Hopefully, while Eurostar hasn’t been moved yet by the widespread public outcry to its proposed policy, it will take serious note of the concerns expressed by leading politicians. CTC hopes they will engage with organisations like ourselves to find a solution which will work for everyone.”