What do you want to use it
What do you want to use it for? Fast club rides? Racing? Sportives? Commuting into town?
Most important thing at this level is to make sure the thing fits! Not just saddle height, which is adjustable enough but top tube length. You want to be able to sit comfortably on it without being too stretched out and too much weight on your hands.
Ordinarily a bike shop will size you properly but it can be pot luck in a decathlon or halfords as the staff member may be new or not fully trained.
If you can spend a bit more you can get some cracking deals on quality bikes that have been marked down from last year. There’s BSOs (Bicycle Shaped Objects!) and theres serious road bikes. At this price point you can end up in either camp.
We’ve got a page on the best sub £500 bike offers. It will give you an idea of the sort of things you could get in your local bike shop (get measured up for your first road bike, don’t buy the first one mail order unless you really know what you’re doing – you’ll want the after sales support from a good local bike shop)