If we started a political party (in the UK, Scotland specifically) where everything was broadcast, would this be better?

A lot of what you're describing is already in force. Generally the "business end" of things- signing things into law, enacting policies, etc, that is already recorded. Debates in Parliament are generally open to the public and officially recorded. So I think a lot of what you are advocating is already documented.

The stuff that's being hidden would probably still be hidden under your system, unless it was more of a 24/7 live feed sort of deal. Politicians often meet with other interest groups, diplomats, etc, behind closed doors and this stuff isn't recorded, nor would it ever be unless we insisted on 24-hour monitoring (which has a host of other concerns). So all that stuff is already there- debates in parliament can be downloaded off their website, for instance.

The catch is that most of the dirty deals, secret arrangements, etc, are all done by the time it gets out into the public eye. By the time a law even reaches a vote in parliament, there's usually been a lot of wrangling and negotiation done to get it there. To get the other stuff out into the public eye, we would need to be recording politicians everywhere they went, which would be problematic.

That's totally impractical. Are you really going to have cameras following every member of the party everywhere they go? Including to restaurants where they talk things over, and into the toilet? Nobody would join.

how would you enforce

everything is broadcast