Seat belt tensioner

The drivers' seat belt on my TF is very slack & doesn't retract very much.
I am due a mot soon & this could be a failure.
Do I need to buy a new mechanism or is there a way of increasing the tension?

You really need to take the T Bar off to see if the belt webbing is binding anywhere, if its not then the belt mechanism and belt needs to be replaced.

It is likely to be an mot failure as it does not retract fully, pull it all of the way out and let it go, it should feed all of the way back.

I got an almost new set of belts from an owner who was swapping for coloured ones and their refund for the old belts was £10 each!! so i got them for £20. My drivers one is worn on the edges and am ready for a possible MoT failure