Jackson Carlaw has resigned suddenly as the Scottish Conservative leader, claiming he is not the right person to lead his party into the forthcoming Holyrood elections. Hours after a combative session at first minister’s questions, Carlaw issued a statement saying he had reached the “simple if painful conclusion” over the past few weeks that the Scottish Conservatives needed a new and better leader. His unexpected departure, only five months after he was elected as Ruth Davidson’s successor, follows a spate of opinion polls giving Nicola Sturgeon’s Scottish National party a hefty lead, putting a fresh independence referendum firmly on the agenda. “[I] simply believe that a new leader will be able, as we recover from the Covid-19 emergency, to make the case for the Scottish Conservatives and the union better than me,” Carlaw said. “That is all that matters.” It is thought that Davidson will make an unexpected return to frontline politics by standing in for Carlaw at first minister’s questions after the Scottish parliament recess, acting as interim leader, until his successor is appointed. First elected to Holyrood in 2007, Carlaw served as Davidson’s deputy for eight years before becoming interim leader after she quit suddenly last August. Her decision was made in protest at Boris Johnson’s selection as leader of the UK party, and to spend more time with her young son and partner. Party sources said senior Scottish Tories had become increasingly critical of Carlaw’s leadership during the coronavirus pandemic, accusing him of failing to hold Sturgeon to account and of tactical errors. With the next Holyrood elections due in May, the latest Panelbase poll put the SNP on 55%, with the Scottish Tories a distant second at 20%. Three successive Panelbase polls put support for independence at 52%-54% – the highest on record. In a statement released late on Thursday, Carlaw said: “In the last few weeks, I have reached a simple if painful conclusion – that I am not, in the present circumstances, the person best placed to lead that case over these next vital months in Scottish politics prior to the Holyrood elections. “Given the importance I attach to the job, I’ve therefore decided to stand down with immediate effect.” His resignation is a serious blow for Johnson, as it will fuel opposition attacks on his leadership. In a clear sign he had cleared that decision with the prime minister, the Scottish Tory party also issued a statement from Johnson. “Jackson Carlaw has been a tremendous servant to the Scottish Conservative party for more than four decades,” the prime minister said. “As an activist, deputy chairman, deputy leader and leader, he has given his all and deserves our thanks for his efforts. It is a mark of his commitment to the cause that he chooses to stand aside at this time and I offer my best wishes to him, [his wife] Wynne and the family.” One source said the looming Holyrood election campaign meant Carlaw had to quit now or stay in post until after the vote, but he had shown increasing signs of unhappiness over the summer, suggesting Carlaw had faced pressure to stand down. Sturgeon tweeted her sympathies: Pundits and party insiders said the most obvious candidate to succeed Carlaw was Douglas Ross, the MP for Moray and a former regional MSP who served for a year at Holyrood before beating Angus Robertson, the then Westminster leader of the SNP, in Moray in the June 2017 snap general election. Ross held Moray in December, surviving when other Scottish Tories lost their seats to the SNP. Ross, a qualified football referee, notably became the first minister to quit Johnson’s government in protest at the Dominic Cummings scandal. He left a post in the Scotland Office after the prime minister’s chief adviser admitted travelling to his parents’ home in Durham during lockdown while he and his wife had the virus. Although no one has yet declared an intention to try to succeed Carlaw, other possible candidates include Murdo Fraser, a senior Tory who lost to Davidson in the 2011 Scottish leadership contest but has favoured splitting from the UK party, or Miles Briggs, the party’s health spokesman. One source said Carlaw suffered from negative comparisons with Davidson, who achieved legendary status in the Tory party after winning 13 Scottish Westminster seats in 2017 and making the Tories the second largest party at Holyrood. “It’s a bit like taking over Manchester United after Alex Ferguson quit,” the source said. “He’s always going to endure unflattering comparisons with Ruth. Senior members of the Tory group had lost confidence in him. The latest polls had really been putting the willies up people. “The [pro-independence] polling and the election next year concentrated people’s minds.”