The weight is a genuine Paul Ysart from the last years of his career (1977 - 1979). The label will have originally been large and circular.
Whether it is worth £375 is debatable, in my opinion. There is a similar weight currently on offer at Sweetbriar Gallery (http://www.sweetbriar.co.uk/weightlist.php?maker=Paul%20Ysart
) - item
46576, with an asking price of £350.
The price of many Paul Ysart weights has risen again in the last couple of years, with some of the 1970s regular output previously obtainable at around £150 to £200 now going for nearer £300!!
However ... If you like it, and can afford it, go for it - but do make sure that it is in perfect condition, with absolutely no scratches, bruises or "flea bites" of any kind. If there are any imperfections, it's not worth the top price. Personally, I also think that a partial label, rather than a complete one, detracts from the value of pieces like this one, which, although always of good quality, are not even true "vintage", being a "mere" 26 to 28 years old.