I live in the UK and have no idea. It's quite likely that we delay quarantine until too late, but when that actually is or how bad is anyone's guess.

Even if the flight isn't canceled, that's going to be a pretty unpleasant vacation. Make contingency plans and expect that there will be a change fee waiver for you to rebook your trip to later.

You might as well roll some dice at this point - going to be as reliable for advice.

I'm supposed to start a short contract there end of March, and I'm considering cancelling. UK seems to be <del>4-6 weeks</del>(EDIT: 2-3 weeks) behind Italy now, and I don't want to get stuck in a different country than the rest of my family, without even an insurance number (apparently, it takes more than a month to acquire one; end of April, I'm betting the country will be in total lockdown).

The UK is only two weeks behind Italy. Look at the numbers.

https://en.wikipedia.org/wiki/2020_coronavirus_outbreak_in_I...

https://en.wikipedia.org/wiki/2020_coronavirus_outbreak_in_t...

You're right; mental brain fart on my end (I was thinking of doublings, but I wrote weeks).

The plane flight/airport will be the biggest risk.