In some countries, what we would call pewter is called just tin, e.g. French étain, German Zinn. (Apologies if the e-acute doesn't display correctly for everyone.)

The actual composition anywhere in Europe is likely to be according to EN 611, which Rowan has already mentioned. (I've just looked it up on the BSI website . EN 611-1 covers pewter (i.e. presumably the alloy) and EN 611-2 pewterware, i.e. presumably things made of pewter.)

"EN" signifies a European Standard, which the national standards bodies are obliged to adopt as a national standard, thus BS EN 611-1 and -2 in the UK, but similarly in France as NF EN 611-1 and -2 (which indeed refer to "étain"), etc. But enough of this digression about European standardisation!

Richard