vauxhall movano 2.5 diesel 2006 gear problems!?

Hi everyone, I wonder if any of you could help me out here, I have a Movano van 2006 long wheelbase with a manual gearbox, With no warning at all I started having problems getting in gear, especially the second & third & later all 5 gears & now the reverse gets in but nothing happens sometimes even with my foot off the clutch! I thought & I was told it's the linkage as it appears to be a common problem with these vans, but later someone looked at it & reckons the cable is working fine & it could a problem on the inside if the gearbox, Could anyone help please? I'm in South Manchester. Regards.