It's a European frame so it is more than likely that it is a 700C - but to be 100% sure, put in a wheel of that size and see how much clearance there is.
Compare these two photos:
The one on the left is a Raleigh that was designed for 27", the one on the right is for 700C (they are the same set of wheels).
I'm running a wheel building class in mid-June if you want to learn mechanics and save some £££ on new wheels.
It's a European frame so it is more than likely that it is a 700C - but to be 100% sure, put in a wheel of that size and see how much clearance there is.
Compare these two photos:
The one on the left is a Raleigh that was designed for 27", the one on the right is for 700C (they are the same set of wheels).
I'm running a wheel building class in mid-June if you want to learn mechanics and save some £££ on new wheels.