Rear Centre seat cushion of Vauxhall Signum wont move?

The following are the instructions from the manual: -Pull the handle beneath the seat, lift the seat and swivel it 180° rearwards until the seat cushion faces down.
All well and good but my centre seat cushion wont move, is it stuck, am I not pulling the seat hard enough? Has anyone had the same problem? Any ideas what it could be and how do I fix it?