Lindsay Lohan moved to London in 2014Reuters

Lindsay Lohan has reignited speculation that she is secretly engaged after stepping out with a large diamond ring for the second time.

The Mean Girls star, who moved to London in 2014, was leaving one of the capital's exclusive night time hot spots, Boujis, at the weekend when she was snapped with the new bling on wedding finger.

Although the man who put a ring on it has yet to be unveiled, it looks like her Mr Right must be generous because experts have estimated the new accessory could be worth £400,000.

"Lindsay's diamonds just get bigger and bigger don't they. She seems to be sporting a 10 carat square cushion cut engagement ring with a half-moon cut diamond on each shoulder," said fine jewellery and diamond expert Lewis Malka.

"Whether Lindsay is set to walk up the aisle who knows, but whoever gifted the actress with this beautiful diamond certainly has a generous side."

Lohan first sent the rumour mill into overdrive in at the end of last year, when she was spotted leaving another London nightclub.

"Lindsay wears the ring all the time, it's a present she bought for herself. It's a beautiful accessory," an insider told the Daily Mail at the time.

But despite the mounting speculation, a source close to the 28-year-old star assured Gossip Cop she's "not engaged".

Lohan previously dated DJ Samantha Ronson and the Wanted's Max George.