Investors have shirked big bets ahead of tonight's parliamentary vote on Prime Minister Theresa May's Brexit deal, with the FTSE 100 gaining just six points to trade at 6,861.

'Unsurprisingly, UK markets are trading cautiously ahead of the event,' said David Cheetham, chief market analyst at XTB.

'With the result expected to be known later this evening, traders are on tenterhooks as they nervously await the outcome, which will no doubt lead to heightened volatility and may well provide the catalyst for an outsized move in both sterling and UK stock futures.'

May's deal is widely expected to be defeated in parliament, and investors have been betting that its defeat will lead to either a softer form of Brexit or its delay, with the pound having risen against the dollar since the turn of the year.

'Failure of the deal to clear the floor opens the gate to a litany of possibilities: a new prime minister, a general election, another government altogether, another type of deal, no-deal and crash Brexit or no-deal and stopping the clock on Brexit,' said George Lagarias, chief economist at Mazars.

Neil Wilson at questioned whether markets were adequately pricing in these potential outcomes.

'It seems unlikely that the market really reflects where we are about to go on Brexit, albeit the lie of the land is more favourable for pound bulls long term, i.e a higher chance of no Brexit or a very soft Brexit,' he said.

'But, similarly, the no-deal risks rise by the day with 29 March just a couple of months away. Either of the extremes are still the most likely outcomes.'

With the vote looming, the pound has dipped against the dollar, down a quarter of a cent at $1.284, while stocks focused on the UK domestic economy edged lower.

ITV (ITV) was the biggest FTSE 100 faller, down 3.7% at 132.7p, as analysts at Liberum removed the broadcaster from its 'most preferred' best ideas list.

House builders gave back some of their recent gains, with Barratt Developments (BDEV) down 1.1% at 502.2p and Taylor Wimpey (TW) falling 1.4p to 155.7p.

Shares betting companies were hit by the threat of tightening regulation across the pond, after the US Department of Justice suggested it would impose wider restrictions on internet gambling.

Shares in GVC (GVC) dipped 2.1% to 680p, Paddy Power Betfair (PPB) fell 1.7% to £61.50p, with 888 Holdings (888) dropped 7.4% to 164.5p and William Hill (WMH) traded 1.1% lower at 166.5p.   

The FTSE 250 edged lower with Provident Financial (PFG) the heaviest hit, tumbling 17.6% to 532.8p after warning 2018 earnings were expected to be at the lower end of market expectations.

This marks the stock’s worst day on the market since August 2017's crash when it announced the departure of its chief executive, suspension of its dividend and an investigation by the City watchdog.

Spirent (SPT), on the other hand, was the biggest 'mid-cap' riser with shares in the telecom business up 10.5% to 138.4p.

It secured a number of key contracts in the final quarter of 2018, with order intake hitting $470 million (£366 million), up 6% on 2017. Revenues also rose 6%, with Spirent reporting profits would range between $75 million and $77 million , ahead of market expectations.

On the Alternative Investment Market, shares in Boohoo (BOOH) fell despite a positive trading update.

The online retailer reported a 44% rise in group revenues in the final four months of 2018 but this failed to rejuvenate investor sentiment after shares were dragged down by a profit warning from Asos (ASOS) last month. Boohoo’s shares were down 7.4% to 180.1p today.

Management upped their guidance for full-year revenue growth to between 43% and 45%, up from their previous guidance of 38% to 43%. 

Helal Miah, investment research analyst at broker The Share Centre, said Boohoo had ‘shown little evidence of the pressures on the consumer seen with other retailers’.

‘As one of the smaller online fast fashion retailers, we have less worries over Boohoo compared to other retailers should the worst scenario unfold from the Brexit process. We continue to recommend the shares as a medium risk "hold" for investors.’