Pekka,
In just this small part of our fine fair land, we have very many local dialects, which if you have never sampled it in the flesh, there is no way you could ever even attempt to understand it.
Just 20 kms from where I live (in the Potteries, Stoke on Trent area), even I have great difficulty understanding what they are saying, even though they still class it as spoken 'English'.
This is the same all over the UK, there are many thousands of local dialects.
Over the centuries, we have been invaded by so many other countries, depending on where they came ashore, the local people incorporated part of the foreigners language into their own local spelling and pronunciation.
There are certain areas of the central and north west of the UK, that is classed the most pure version of real spoken English, purely because the invaders thought we were not worth bothering with, so never came that far inland.
Bogs