Thanks for the various tips.
I have now treated the mat with a third application of Vanish Carpet Foam ((thanks for the tip Adrian) and it seems to have done the job.
I have also invested in a far better quality travel mug to ensure there are no further incidents.
Also, whilst visiting the local (and excellent) Halfords I noticed they have some very good looking rubber mats on sale.
I am very tempted to get some for my tintop for the winter.
