It doesn't sound like typical FFS, which doesn't come and go. Once the filter case has loosened enough to reduce fuel pessure, the engine won't start again. You need to be sure whether your filter is the later type before opening up the tank for further investigation.
With the rear seat out of the way, remove the circular hatch on the nearside floor. This will reveal the top of the filter module. Check whether the white plastic top has two loops or not. If the loops are present it's the earlier filter that doesn't suffer from FFS.
There's a photo of the earlier filter in Posts 5 and 6 here:
http://www.the75andztclub.co.uk/foru...d.php?t=110917
This thread shows the later FFS type filter and how to fit the orange clip:
http://www.the75andztclub.co.uk/foru...d.php?t=158626
TC