The British Isles and western Europe in general do not have many breeding bird species compared to other parts of the northern hemisphere. This is said to be due at least in part to the history of glaciation and the massive extinction rates in Europe during glaciation. North America by virtue of the north-south orientation of her mountain ranges and eastern Asia by virtue of large relatively ice free refugia during glaciation did not suffer extinction rates as high as in Europe (where the major mountain ranges are predominantly east-west in orientation and their frozen peaks prevented southward escape for many species). Of course, human land use may also have something to do with this. A famous statistics is the ratio of tree genera in boreal forests in Europe : North America : Siberia that comes out approximately to 1:3:6 (i.e. for every tree genus in a European boreal forest there are three in a comparable forest in North America and six in eastern Asia). Nonetheless, there is some great birding to be found on the British Isles and they do get a lot of vagrants and rarities blown in from North America, Siberia and elsewhere and birders here focus strongly on finding rarities. Of course, many now famous birding traditions like twitching have their origins in the U.K.
It is not hard to find ponds or small lakes Some natural some not) in the U.K and water birds abound both inland and in the coastal areas. One of the most commonly seen, even in urban parks, is the Mute Swan. As this species has been introduced into other parts of the world such as North America, it will be familiar to many outside of Europe with their characteristic red beak and black knob atop the upper mandible. I have always wondered why they are called Mute Swan since they can be very loud at times (maybe because they seem to make more snorts and grunts than the more bugle like calls of other European swans??).
As large as the Mute Swan but with a yellow rather than red beak is the Whooper Swan that breeds in northern Europe and winters in the U.K. Note how the yellow on the beak extends forward past the nostril in a point. This bird had a broken wing and was over-summering in Britain as it could not make the migration north.
The handsome Red-legged Partridge is also introduced into Britain, yet another example of the long-standing practice of introducing game species outside of their natural range.
The Eurasian Curlew is much more widely distributed than the North American Long-billed Curlew. Note the white rump and underwing.
Lesser Black-backed Gull is a Palearctic species that is becoming increasingly common in North America by leaps and bounds and may now breed there. In the U.K they are extremely common! The first photo shows an adult and the second a juvenile (wit ha Black-headed Gull in the background). The British birds are the graellsii subspecies which are not quite as dark as the fuscus subspecies.
There are quite a few pigeon / dove species in the U.K, the most common being the Common Wood Pigeon
The Great Spotted Woodpecker is the most common and easiest woodpecker to see.
The beautiful European Green Woodpecker requires a bit more effort but is well worth a search!