Thanks for the responses, chaps (and chapesses).
Thanks for the advice using the vinegar/ baking soda. One of those is acidic, the other alkali?? but as long as it works thats fine. I did try Vanish, but it did diddly squat. It could be that my old t-shirts are passed their best now, but I will try it the new ones.
I sometimes feel a right dirty person, not washing my kit straight away, Im like that with my shoes too. The poor old trail shoes dont get washed or rinsed from the day they come out of their box til they are thrown away. The other week, there was grass growing out of them (I jest not) as I had left them wet and muddy in a warm place for several days.
It is of great comfort that Im not the only person with revolting kit.