Do they have glass roofs as well?
The B&W though small might be OK, the port "may" cause some problems and make the bass sound a lot louder.
Your axil modes for example, (the modes that travel down the room) are 34Hz 48Hz 86Hz, I don't know what B&W go down to, but maybe the 48Hz may excite them and being glass it may exaggerate the problem, I think in conservatories you just put garden type furniture? (Not sure, not from UK)