Is the manifesto a legal / enforceable document?

The manifesto is not a legal document. It is a sales pitch to do this and that...

You have to then question are the promises feasible, desirable , realistic to act upon in the current climate?

You then have to choose the candiadate who you believe will fulfil the promises. Some are really unrealistic as there are better alternatives or focus

That being said, the manifesto is a testament of their promises. If they fail to fulfil them, either make your vote counts now or wait another 5 years to vote against them​​​

No, I guess it is only broken promises then, not broken law.

because they state possibly "we work on...", "we will ..." in the papers.

Similar to Unit Trust managers, true ? ;-)