The point at which Bitter becomes something else is difficult to define. It is generally accepted that once 4% alcohol by volume (abv) is reached, you are into Best Bitters and by 4.6% abv you have a strong or premium bitter. Much beyond 7% is into the realms of barley wine. Generally speaking as beers get stronger they get sweeter because unfermented sugars are likely to linger about. Some strong ales however are also noticeably hoppy or dry so you cannot be doctrinaire here.
Greene King Abbot Ale (5%) is the best known strong bitter in these parts; the recipe was changed in 1995 and it is also fermented longer (7 days, enabling the Brewery to claim that it is blessed by the Sabbath). The majority view is that the change was for the better and it certainly no longer has the hangover-inducing side effects it had before. Charles Wells Fargo is also 5% but it is now a winter-only brew. It is well worth seeking out for its complex flavours and dry finish.
Many would claim that the best Premium Bitter in the country is Ind Coope Burton Ale (4.8%), a gloriously rich but hoppy beer which is now under threat following the purchase of the Burton Brewery by Bass, whose own Draught Bass (4.4%) is generally a cloying shadow of a once great beer.
Barley wine was traditionally a bottled beer, sold in third-of-a-pint nips. Some like the fearsome Marstons Owd Rodger and Robinson's Old Tom have always been available on draught. Now many micros offer a "headbanger" as well. One of these, Cottage Norman's Conquest, was Champion Beer of Britain a couple of years ago.
Beyond 10% things just get silly as brewers compete to produce "the world's strongest ale". A beer like Parish Baz's Super Brew (23%) will actually be completely undrinkable.
Stouts and Porters are often confused both being dark, heavy beers but they are in fact quite different. The distinctive characteristic of Stout is its roastiness, derived from well-toasted barley malt, but most Stouts are also truly bitter. Guinness is something of a by-word for Stout although the draught version available in pubs is a keg product. A number of micro-brewers produce Stouts with B & T's Edwin Taylor's Extra Stout from Shefford being an excellent local example - try it in the Live and Let Live.
Porters are generally weaker and sweeter than Stouts. This is an historic beer style which first became popular in London in the early eighteenth century. It had a particular following amongst market porters, hence the name. Porter is not easy to find outside of beer festivals. Greene King's seasonal Black Baron is essentially a porter and some would argue that City of Cambridge Jet Black is more of a porter than a Mild.
Finally, lager. This is in fact another classic beer style, but a continental rather than a British one. The word Lager means store, because the fermentation and storage periods are long, slow and cold. Proper Lagers like Pilsner Urquell and Budweiser Budvar (both from the Czech Republic) are amongst the world's great beers. The sad, fizzy water that is British-brewed lager has next to nothing in common with the genuine article.
Some micros have dallied with the notion of brewing cask-conditioned lager and some of the results have been intruiging. Schiehallion from the Ochil Hills in Tayside for instance is a fine hoppy brew which uses genuine lager yeast and is given a proper storage period. Be good to see a local brewer having a shot.
Brief mention may be made of some of the other styles - wheat beer, increasingly popular in Europe; fruit beers, a Belgian speciality; beers with a particularly unusual ingredient such as coriander, heather or bog myrtle. The fact is that beer offers an endless variety of taste experiences and deserves a lifetime's careful and dedicated study. So what are we waiting for? Mine's a pint!