A new poll gives yet another lead to Sadiq Khan in London – as the Labour Mayoral candidate launches his election broadcast setting out why he wants to win.

Khan is eight points ahead of Tory rival Zac Goldsmith in the capital, and voters say they trust him more on issues of crime, housing, unemployment, fares and managing public transport. The Opinium poll for today’s Evening Standard gives Khan a eight point lead on first preferences, by 35 per cent to 27 per cent, a lead he maintains when second preferences are taken into account, with 54 per cent to 46 per cent.

While this adds to a long trend of leads for Khan, there are reasons to be cautious.

Firstly, Goldsmith holds a small lead in outer London boroughs – mirroring an electoral strategy of targeting these voters that led Boris Johnson to two victories.

Secondly, the number of “don’t knows” could yet play a big factor, with both campaigns kicking in for the final few weeks of the campaign. Nearly a quarter – 24 per cent of voters – say they do not know who they will give their first preference to, rising to 28 per cent in outer London and including 31 per cent of all women – among whom Khan otherwise has a 10 point first preference lead.

Turnout could also play a big factor. Nearly half – 49 per cent – of voters in today’s poll say they will vote, which would be a huge rise from the 38 per cent turnout in 2012 and an increase even on the previous high for a Mayoral election of 45 per cent in 2008. Generally, it seems Labour voters are more likely to overstate to pollsters their likelihood to vote, and it should be noted that Goldsmith has a lead among the over-55s, who tend to be reliable visitors to the polling booth. By contrast, Khan has a huge 26 point first preference lead with 18-24-year-olds, who are much less likely to cast a ballot.

The polling lead comes as Khan reveals his new broadcast advert, which will air on BBC One and ITV tomorrow night.

The video has been emailed out to London Labour supporters this afternoon, and features Khan laying out his vision for supporting social mobility, keeping transport fares down, tackling crime, and being “the most pro-business mayor London has ever had”.

You can watch the video here: