The Scottish National party has appointed a new auditor more than six months after the previous firm quit, as senior leadership moved to reassure members that the looming accounts deadlines in Scotland and at Westminster will be met. The SNP leader, Humza Yousaf, confirmed that the party had signed a contract with AMS Accountants Group to work on both the party and the Westminster group’s accounts. It emerged for the first time earlier this month that Johnston Carmichael, the party’s auditors for 10 years, had quit last September – a fact Yousaf revealed he discovered only after he became leader. Announcing the “welcome news” on Wednesday morning, Yousaf said: “There is hard work ahead, but it is really encouraging to have them on board as we work towards challenging deadlines.” The new firm faces a particularly tight deadline to submit audited accounts for the SNP’s Westminster group by 31 May, or it risks losing £1.2m of public funding, known as Short money, which is paid to opposition parties to assist their parliamentary work and is calculated according to how many MPs they have. But the party’s Westminster leader, Stephen Flynn, said he was “confident” the deadline would be met. “Throughout this period, SNP MPs have remained focused on standing up for Scotland and supporting our staff,” he added. Flynn has previously denied claims from his predecessor, Ian Blackford, that he knew the SNP had no auditors in place, insisting he first learned they had quit when he saw media reports. The party faces a further deadline of filing audited accounts with the Electoral Commission by the beginning of July. Yousaf thanked the new party treasurer, Stuart McDonald, for securing the auditors’ services. McDonald replaced Colin Beattie less than a fortnight ago after Beattie stepped back from the role after his arrest as a suspect in the ongoing police investigation into the party’s funding and finances, which has left the party in turmoil. Operation Branchform, which was set up in July 2021 to investigate allegations the party had mishandled more than £600,000 in donations, has also included the arrest of the former chief executive Peter Murrell; a two-day search of the home Murrell shares with his wife, the former first minister Nicola Sturgeon; the seizure of a luxury motorhome bought by the SNP from outside Murrell’s mother’s home in Fife, and the search of the party’s headquarters in Edinburgh. Murrell and Beattie were released without charge pending further inquiries. Last week, returning to Holyrood for the first time since Murrell’s arrest, Sturgeon described it as her “worst nightmare” but reiterated that the police investigation had played no part in her decision to stand down as SNP leader. McDonald said the appointment of new auditors represented “a significant step forward of the party’s stewardship under the leadership of Humza Yousaf”. Industry experts have told the Guardian it is increasingly difficult for smaller organisations to find affordable auditors because of a lack of capacity in the sector, smaller clients being considered less profitable, and tightened regulation after a series of auditing and cross-selling scandals in recent years. This has resulted in auditing firms putting more effort into larger clients. A more challenging regulatory environment also means that auditing firms are much more risk-averse.