Well thanks for the varied advice which I appreciate.
I did go to look at the stain

and I did think that it was not going to be removable....
However I had a product calle 'Krudkutter' on board. American, (now there's a surprise) invented by a Brit who couldn't get funding here so moved to the states and became a multi millionaire

It actually worked really well and the cutomer was well chuffed, hence I'm back in January to finish the job.
Oh, and of course she had alreay had a go with the old 'Vanish & Bucket of water' lovely big water stain and loads of foam.

Many thanks
Les