Rightmove shares fell on Monday after the British property website rejected a fourth takeover bid by Australia's REA Group.

The FTSE 100 group told shareholders the latest bid, which was worth roughly £6.15billion in total, was 'unattractive' and continued to 'materially undervalue' Rightmove and its prospects.

Rightmove also revealed it had rejected REA requests for an extension of the 'put up or shup up' deadline, meaning the Australian firm has until 5pm today to make a final takeover attempt – or see the door slam shut on its efforts.

The latest bid comprised 346p in cash, 0.0471 REA shares and a special cash dividend of 6p per Rightmove share, marking an increase on the third offer of around 3 per cent.

REA, which is 62 per cent owned by the Murdoch family's News Corp, says a takeover of Rightmove 'would look to enhance the UK property experience for buyers, sellers and renters', supporting Rightmove's vision 'to give everyone the belief they can make their move'.

But Rightmove chair Andrew Fisher said on Monday the board is 'confident in the standalone future' of the group, amid 'very significant opportunities for future growth'.

The firm told shareholders that REA requests for further due diligence information and an extension to the bid deadline would not be in Rightmove's best interests.

Fisher added: 'The last few weeks have been very disruptive, as well as unsettling for our colleagues.

'To the extent REA wants to put forward a further proposal, I urge them to submit a best and final proposal ahead of today's 5pm PUSU deadline such that we can bring certainty to this process.'

Rightmove shares were down 2.4 per cent to 652.4p in early trading on Monday. Takeover speculation has helped propel them 17.4 per cent higher since the start of September. 

REA are yet to comment on the latest bid rejection.