Cucumber Merlin height problem.

[George the Pigman]

I bought some Cucumber seed - Merlin variety and have a healthy plant growing in the greenhouse. However it is only about 2 foot high and doesn't seem to want to continue up the netting I have set up for it although it does produce cucumbers at the nodes.
Have I bought a variety that is smaller than usual?
The seed companies that sell it don't give any information about the height or suggest it is anything other than a standard climbing variety.

[George the Pigman]