Dave,

The Labour party cannot be antisemitic. It is not in it's manifesto.

Exactly true. It has a serious problem with some of its members, but the party itself can not be said to be anti-Semitic and no-one has suggested it is.

A footballer's contract is different. A manifesto sets out the aims and views of the Party.

Steve,
Keith. What a vote-winner it would surely be if a political party stated that "we are racists" in its manifesto!

It would not be. British people would shun it, but UKIP is very popular.
Parties set out their beliefs and aims in their manifesto.
If there is nothing racist in it, how do you know they are racist Steve?
Presumably not voices telling you, so where does your belief come from?
If it is based on no actual facts, it is just prejudice against holders of different views to your own.