Strike action at McDonald’s is to spread to outlets across the country in the coming months, following the lead of workers at two restaurants in the south of England.

Dossiers on claims made by staff, ranging from the company’s alleged failure to provide protective equipment for workers using grills to allegations about management mishandling sexual assault claims, are being compiled by trade unionists. The September strikes were the first at McDonald’s since it opened in the UK in the 1970s.

Branches in the north-east and north-west of England, Yorkshire, Scotland and Wales are expected to be involved in the next stage of attempts to build up a union structure at the company. About 40 staff went on strike in September at two restaurants in Cambridge and Crayford, south-east London, after a ballot in favour of industrial action amid concerns over low wages and the use of zero-hours contracts.

The fast-food chain has been one of the biggest users of zero-hours contracts in Britain, although it has this year started offering workers the option of moving to fixed hours.

“We are looking at moving [the strikes] right across the country so we are planning very carefully how that will be done and how workers can take part,” said Ian Hodson, national president of the Bakers, Food & Allied Workers Union, one of Britain’s oldest trade unions.

Workers in managerial positions are also among those who have come forward to voice concerns confidentially about issues including burns sustained from grease popping from grills.

At least one McDonald’s worker in the UK has also alleged that the company did not respond adequately to claims that she was sexually assaulted by a more senior member of staff.

Tom Holliday, a 25-year old a shop steward at a branch in Cambridge told the Observer that awareness of the union had increased both among colleagues and customers since the strike.

“Things have settled down now and we have moved into having regular meetings to talk about issues in the work place and how we can win small changes,” he said “We didn’t have the correct protective equipment and the company has now acted on that and given us the correct equipment. We needed visors and aprons in order to clean out filters. Since the strike we put in a complaint and it was immediately brought in.”

He added that action had also been taken in relation to customers who had been rude and aggressive towards staff.

“In the past rude customers were completely ignored. The reaction would be to give them free food to get them to go away. One particular customer would threaten people and we had consistently made the point that this person should be banned. As a result action has been taken.”

Holliday, a father with a young son, believed that the expansion of efforts to build a union presence would help moves for pay claims.

“On a personal level it has been empowering to take the action and the support has been much greater than we expected. We still get people coming through in the drive throughasking how it is going and what is going to happen in the future.”

A spokesperson for McDonald’s said: “Health and safety is of paramount importance to us and we place great emphasis on our employees’ safety. We have robust training and processes in place for our staff and our restaurants are regularly inspected by environmental health officers to ensure our high standards are upheld.”

“We’re unable to comment on individual HR cases, but would, of course, take any accusation of sexual harassment extremely seriously.”