maybe it is a Rhododendron

Picture found in the link below

Here is a link that might be useful: Rhododendron 'Arnoldiana

The type, whether rhododendron or evergreen azalea, is relatively unimportant as long as its bloom color and mature height are you want to achieve. A good local nursery is probably the best place to get recommendations for well-adapted and vigorously growing varieties.

What is important is 25 years or so of careful pruning, pinching, fertilization, pest control and other meticulous care.

The azalea kosmos or azalea girard crimson might be a good choices. Your plant hardiness zone make a big difference. Being in London, your zone is 8. Remember that summers in London, UK zone 8 are different than the long hot summers of zone 8 Alabama or Georgia, USA.
Do some research about growing azaleas or rhods in your specific climate and grow away! I hope you enjoy growing your own beautiful flowering hedge:)

I've seen just one hedge maintained that way over many years, may have something to do with the care involved :)

Same approximate weather as your zone, there is an evergreen azalea hedge either side of a long sidewalk leading to the doors of a church that I pass on my way to my mothers house about 100 miles from here. I don't mean to discourage you, but it's quite formal, appropriate in front of the very formal building. It looks wonderful for a few brief weeks in Spring, is pruned after new growth follows blooming where it then looks a little sparse, browning (or woody, I haven't parked to inspect) in some areas where it's been cut back to continue the angular lines, will fill out again closer to late summer.

I wouldn't presume to impose my personal taste on you, but other than those few weeks around Easter, I don't find it an effective use of azalea. I'd rather see a boxwood shaped that severely lining the walk if hedging were wanted there, and azaleas in their natural shape planted nearby.

I'm sorry but I can't tell you specifically which azalea has been used, only that its a deep rose pink, evergreen, and clearly tough as nails as it's endured that treatment many years now.

Would look better if plants had natural spreading mound shapes instead of having been forced into a boring and stifled rectangular configuration. Effect would be much more elegant and impressive.

Most rhododendron and azalea people shudder at the thought of pruning them into a hedge. However, the Japanese are into this on a grand scale. If you want flowers you MUST prune each year immediately after blooming each spring. Encore azaleas are totally out since they keep on blooming. Also, I would guess that Encore azaleas do not do well in the UK since they like more sun. One good azalea that is red and likes to be pruned into a hedge is:

'Hino Crimson', Early, -10F, Low/Med. Bright crimson flowers unfold in April, and holding their color well. This attribute, coupled with sun tolerance and red winter foliage, makes 'Hino Crimson' an excellent all around choice. Planted in the open, it grows to a dense 2.5' mound, although it adapts well for use as hedging. I don't know how well it does in the UK, but I would guess it would do well.

I had Hino Crimson. The hedge does look like it.

Since this is a low broad one a sheared hedge of it is not likely to have much height. We have a lot of it in my area and garden references from similarly cool Britain do list and describe it. Sources can be found in the RHS Plant Finder, which has an online version.

Here you would not have to look very far to find it, especially as this time of the year.

Not sure if Satsuki (or Gumpo) azaleas would do well in England, but they tend to grow low and spreading without much need for pruning. Flowers are large and sparser than Kurumes, etc, but their form is really appealing. One of my favorites is 'Chinzan'.

Thank u for all your comments. I am using Hino Crimson and it I working great.