David Cameron
The prime minister has been handed a boost by the latest poll results as Remain takes the lead Stefan Wermuth/Reuters

Prime Minister David Cameron has warned the electorate against voting to leave the EU ahead of the crucial referendum on 23 June, saying it would be an "act of economic and political self-harm." Cameron made the case for staying in the bloc as the gap between the two camps narrow.

Remain has been handed a boost in the latest Telegraph poll with 51% of voter support – up 4% from last month – compared to 44% who backed the Leave camp, a decrease of five points from last month. Only 5% said they were undecided on how they would vote, but said they would be more inclined to opt to stay in the EU.

Writing in the Telegraph, the prime minister highlighted the dangers of leaving the EU and urged the British electorate not to "rip up our membership of the single market – a market that Britain practically invented – in the hope of renegotiating a new arrangement." Last month London Mayor Boris Johnson – who has thrown his weight behind the Leave camp – pointed to Canada to make his point about a brighter British future outside the EU.

Johnson claimed Canada was an ideal example of a country that has free trade deals with the global community while keeping control of its borders. "If we take the Canada free trade deal as a guide, we know it would be damaging for agriculture and manufacturing," Cameron wrote. "Our beef and pork exports would face tariffs, and our car manufacturers forced to comply with rules imposing additional costs based on where they buy their components."

Cameron argued that even if the UK struck a deal similar to Canada's (which runs to over 1,500 pages – 800 of which are reservations and barriers), "no real-world alternative to EU membership would come close to what we have now. Even the most ambitious trade deal on services the EU has ever struck – with Canada – falls radically short of single-market access."

The latest poll figures will be welcomed by Cameron, with 39% of those surveyed saying the Remain camp is "more credible and trustworthy" compared to Leave (32%). Number 10 believes that the out campaign is lacking a consistent message, according to reports.