Here in the U.S. and, I would expect, in the U.K., Fredrix Pre-Stretched Watercolor Canvas works fairly well. One must fix the painting when completed and some artists I know still prefer the superior brands of water color papers.
Even ordinary cotton canvas could be used, but must first be embellished with an acrylic medium and use care to use a varnish or other covering once completed... Mrs. C uses Krylon #7120 Finish Spray...