Hoping that someone here may be able to help!

I recently bought a VW polo from a private seller (2007 1.2l engine 3 cylinder). I knew that some work had been done to the engine and the previous owner was able to provide evidence of this. This included a head gasket set, new timing chain, inlet valves, exhaust valves, cylinder head bolts and spark plugs. The cylinder head was also taken to an engineer for a skim and valves & seals were changed. While they weren't able to tell me what had happened, the car was driving perfectly and didn't seem to have any issues.

I live in London so most driving for the first few weeks was at a max speed of 40mph. I took it out for its first motorway drive a few weeks ago. 10 mins into the M25 and the check engine light started flashing and car went into limp mode. The engine light stopped flashing when I'd pulled in at the services and switched it off for a few mins. The AA diagnosed a misfire in Cylinder 1. They replaced the ignition coil which cleared the error code and the car was driving fine after that.

Took it out for its next motorway drive at the weekend only for the same thing to happen again. AA ran their diagnostics and it showed another misfire in Cylinder 1. They chose not to sell me another ignition coil and advised I drive home slowly, bringing it to my local garage asap.

My local garage have advised it will be a case of trial and error to see what the problem is. I don't live near a motorway so will be difficult to know if the problem has been fixed until I bring it out again. I messaged the previous owner to ask if they'd had the same issue. They said they regularly did long-distance trips, travelling at 70mph with no issues. It's difficult to know whether to believe them or not but seemed genuine enough!

Does anyone know what this could be or how to solve it? I'm hesitant to spend any more money on the car (recently had it serviced and two new tyres!) if I'm fighting a losing battle.

Thanks in advance!