Entry level road bike?

The cheapest we've seen that looks like it might do the job and be fun to ride is the Decathlon B'Twin Sport 2 for £229. Decathon's bikes tend to be good value for money and pretty well sorted. Evans do the Dawes Giro for the same money.
http://www.decathlon.co.uk/EN/sport-2-16v-42393911/
http://www.evanscycles.com/categories/complete-bikes/road-bikes?page=1

Going up a notch Specialized and Giant are two other brands that have always really punched their weight at the entry level delivering good bikes at excellent value for money. Expect to pay around £400 - £500 (the latter being closer to list). The Trek 1.2 at £450 looks pretty good too. At this time of the year it is also worth looking around for good deals on old stock.

You could also consider buying secondhand - your money goes a lot further then.

If you live within reasonable distance of a Decathlon I would go for theirs as they have a free 3 month service included in the price.

I had the entry one for a couple of years before selling it on and it is still going strong being used by someone as their commute bike.

It is never going to be the lightest bike in the world, but it will be reliable.