Solid wood flooring problem

[sg1234]

We had solid wood flooring laid over existing floorboards about 5 years ago. It must have been laid too tight as every summer it has bulged slightly as the weather has warmed up but then settled down again in the winter. This year - I'm guessing with the combination of heat plus dampness in the air it has bulged a huge amount and really needs some attention. There is a five foot gap between joists and solum so we are fairly sure that there is no dampness from beneath.
Is it likely that this is just being caused by the damp atmosphere (we're in Glasgow so damper than most) and if so would it be solved by cutting through one of the planks that divide the two rooms it is laid in and creating a gap? I was thinking we could put in a metal room divider to cover the gap. It would look rubbish but would be better than what we have at present. Any good ideas?
SG