Hardly at all. Stop listening to scaremongering news reports that suggest the UK has been obliterated.
Yes there were many areas that were badly affected but the recent dry weather has dried most of it up now and it will have no effect on your holiday. You need have no concerns on that issue.
The railway line which was washed away at Dawlish has been rebuilt and just reopened.
You do have to wonder about the effect of sensational journalism on people who can't look for alternative sources of information. To put it in perspective - a mere 8500 claims for insurance against fkood damage were submitted - out of a population of 65 million !
A small amount of flooding in the upper reaches of the Thames, miles from London, was described in the press as 'London Flooded'. DUH
Everything is normal.
The worst of the flooding was mostly confined to rural areas in Somerset, and for a while parts of the River Thames to the west of London. Storm damage did occur in other areas, most notably the South and South West of England but conditions have improved considerably in recent weeks.
Unless there is another severe weather event between now and September ( something no-one can forecast ) you really need have no concerns at all.
There's a documentery just out, called "Noah " which is worth seeing.
It's pretty much normal for the UK and no problem apart from the devastation to individuals affected. It certainly won't affect your travel plans. I was in S Africa when the floods hit and thought that I was coming back to a subterranean world. You can't always believe the extent of what's reported
The reporting has probably been fairly accurate (pictures of engulfed towns and villages are what they are), but when people see pictures of widespread flooding they don't know just how large an area it covers. Given the truly devastating nature of some floods in the US in fairly recent memory, in particular New Orleans, it is not really surprising if people from the US are unsure of the scale here.
BTW, many people could not get insurance after the previous rounds of flooding or had to settle for a large excess, making smaller claims pointless, so the number of claims is not an entirely accurate guide to the extent of the damage.
I have to say that BBC World rather gave the impression that the entire UK was threatened when the Thames Valley was mentioned! Feel free to travel here this summer