Civil servants who continued working during yesterday's national strike have revealed they were told to pretend to be answering machines to cope with an overload of calls from the public.

Staff at the Department for Work and Pensions in Carlisle said today they were given a brief script to read out before hanging up, in the style found on telephone answering machines.

The instruction by managers was initially leaked on Facebook after chitchat between strikers and colleagues who had stayed at work. One worker said: "To begin with, we all found it hard to keep a straight face, and occasionally, I slipped up and I ended up giving my name to the person who was calling."

The staff said their fake-robot message was issued for peak lunchtime, between midday and 2pm. The script read: "Due to the high volume of enquiries we are currently experiencing we are unable to take your call. Please call back later."

The clerical worker said: "I believe the idea was that we would have difficulty coping because of the strike, but it just seems like a silly way to handle the problem. We were asking why they didn't just prepare a proper answering message saying we couldn't answer calls because of the industrial action. It just seemed wrong to hang up on people."

A spokeswoman for the DWP did not confirm the instruction but said: "Due to a high volume of customer calls yesterday between 12pm and 2pm some customers were asked to call back after 2pm. Otherwise the majority of our customers had their calls and requests dealt with immediately and in the usual manner."

On the picket line outside the Carlisle offices, which serve Cumbria, Jennifer Wright, branch organiser for the Public and Commercial Services Union, said: "Pretending to be an answering machine is hardly good customer service. Some people may have been sitting waiting for the phone to be answered for 10 minutes – and they're not ringing up just for a chat, they've usually got important questions."