SNP volunteers at a newly-opened campaign office in West Lothian have resorted to only working in pairs after two of their cars were keyed and two suspicious-looking men filmed them entering and leaving the building.

The party office in Bathgate – which only opened last week – is set to become the election campaign hub for local MSP Fiona Hyslop, the Culture, Europe and External Affairs Secretary at Holyrood.

Police confirmed yesterday that they were investigating the incidents, which have left female volunteers fearing for their safety.

Fran McNabb, a volunteer who is acting office manager, said the first incident happened on Monday night, when a constituency meeting was held in the new rooms. She told The National: “When we came out of the meeting, one of our ladies who is disabled saw that her car had been scratched – a key had been run along two panels of it.

“Then on Wednesday my car was parked outside the building, complete with SNP stickers and the like and it was keyed along one panel. While I was at the police station reporting that, there were two men dressed in hoodies standing outside the building with a mobile phone filming the windows and the entry to the building.”

McNabb said she then reported the incident involving the men to the Police Scotland call centre, where a call handler told her they were not confident about catching anyone for the vandalism. However, she added: “She said she was concerned about the sinister nature of someone standing around filming the windows and doorways.”

She said the number of volunteers varied depending on what activities were going on, but she had been in the office alone on several occasions. That, however, had changed.

“As a result of this incidents I’ve put a procedure in that if we don’t have a minimum of two people in the building then it stays closed for safety issues, because I’m concerned about this now,” said McNabb. “If I get there in the morning and there’s nobody to give me a hand, I go in and shut the door and lock it and wait until someone else comes in before we open the doors.”

McNabb said efforts were being made to obtain CCTV footage from the owner of the building to try to trace the vandals and the men who were filming. “The guys who were filming had walked up and down outside the building for a good few minutes, so hopefully they’ve been caught on CCTV,” said McNabb.

Hyslop told The National: “We have had great support from our volunteers to our new campaign hub and we want that to continue, but these vandals must be caught.”

In a statement, Police Scotland said: “Police in West Lothian received two reports of vandalism to cars parked in the Glasgow Road area of Bathgate on Monday 18 and Wednesday, 20 January. Inquiries are currently ongoing and anyone with information is urged to contact Police Scotland on 101 or contact Crimestoppers anonymously on 0800 555 111.”

Officers are understood to be treating the vandalism and the filming of the office as separate inquiries.