So what do the parties believe on 'key' moral issues?

There's a paper downloadable here produced by the Christian institute. It examines how the parties and their leaders have behaved in the past over certain moral issues for society. Sadly the scope is narrow, and omits certain key areas such as poverty and war, covering just the 'hot button' topics.

I would view it like licking your finger to see which way the party morality is blowing. There is every possibility that some will find a particular action immoral, while others will find those actions very moral. An example might be the the Liberal Democrats requirement that church schools teach homosexuality to be "normal and harmless" and they should not teach that homosexuality was morally wrong.

There's a lot to read, but it may be a useful resource.