A hacker has hijacked a Liberal Democrat website with a message to Nick Clegg not to break his promise on tuition fees.

The site – www.liberaldemocrats.co.uk, which is registered by Liberal Democrat headquarters – is linked to a YouTube video in which Nick Clegg repeatedly states that he will "resist, vote against, campaign against, any lifting of the cap".

This week, the Liberal Democrats broadly endorsed the Browne review, which called for the cap on tuition fees – currently at £3,290 – to be removed. One of the key election pledges of the Lib Dems was to phase out tuition fees over six years.

"Keep your promises Nick", the website states. "We haven't forgotten." The site has had hundreds of views and already has dozens of comments.

One states: "It was obvious that the lib dems were incompetent from the start of the election, with the torys it was obvious if you read their manifesto that there policies were gonna break the country down, not that they stuck to it :\ infact what they are doing is worse than what they proposed.."

The New Statesman said the website is not the official website of the Liberal Democrats, but is registered to 4 Cowley Street, London, SW1P 3NB - which is also the address of the Liberal Democrat headquarters in Westminster.

An NUS spokesperson said: "It's great to see the Liberal Democrats are so keen to highlight Nick Clegg's fees pledge."

A Liberal Democrat spokesman said: "We are trying to resolve this."