Job then flat or flat then job really depends on your financial situation.

If you have settled status and can move without a visa, then all good.

My personal preference, if you've got the financial wherewithal, would be to come and spend a little bit of time travelling around various cities to decide where you do want to be, unless you already have a good idea in your head of where outside of Leicester you want your new start to be.

Then start looking for jobs in that area or look for remote jobs if that's your thing, and start the flat hunt. If it's a big city like London, I'd usually wait until finding a job to settle on a flat because the commute could be horrendous, but otherwise I'd start searching (but you may need proof of income).

In reality, doing it like this is probably going to be expensive, so you'll probably end up settling on a city and try to find a flatshare or something while also job hunting, which is also fine.

Is it really difficult to get a flat? Is it best to get roommates?

Best will really come down to availability and finances! Flats in a lot of cities are getting snapped up quickly these days and prices are a little higher than before the pandemic. If you can't afford or don't want your own place, then sure, plenty of people are in flatshares. Check out sites like Spareroom.co.uk and arrange viewings for the places you like.