you should be careful using matweb.com (or any online source) - sometimes the young's modulus figures just don't make sense. I forget precisely what material I was looking at the other day (some kind of steel I think), but the young's modulus from matweb was listed as 133GPa, while all other sources that I checked put it closer to 200GPa.
Where have you found BS4360 material? I thought it had been made obsolete years ago by BSEN 10025. According to the British pressure vessel code the value for Young’s modulus is valid for all carbon steel.
You will find different codes will quote different values, these are minimum specified and may well be quite different from the actual values gained from a tensile test.