Sidestep will be a US-only site after Kayak put a halt to any global ambitions for the brand following its takeover last month.
UK and European users can now only search for fares and hotel prices on Sidestep.com in US dollars.
Kayak said it is committed to retaining the two brands in the US – where both have sizeable user numbers and history – but any expansion into new territories will be under the Kayak banner.
An exclusive white label deal between Sidestep and mobile phone giant Orange in the UK was also switched to Kayak following the acquisition, officials confirmed.
Sidestep created a London office in 2006 for its official launch in the UK and Ireland, headed by European managing director Kevin Eyres.
Eyres left in September 2007 to pursue other interests while European business development director Tim Simmonds parted company with Sidestep following the takeover by Kayak three months later.
Kayak has local sites in France, Germany and Spain, with plans to launch an Italian version in the coming months.