There are many different Englishes and many dialects within those.
We have British, Irish, American, Australian, Jamaican and Carribean, South African Englishes. Would you divide the English spoken in Pakistan and Indian or group them as South Asian English? Then we have Singlish (Singapore English), and other East Asian forms, like Hong Kong.
To make matters more compicated, British English can be divided into the nations making up the UK (England, Scotland, Wales and Northern Ireland).
These can then be subdivided. England has recognisable dialects like Geordie (Newcastle), Scouse (liverpool), Mancunian (Manchesster), Cockney (London), Estuary (a new one emergin as an alternative to Cockney in London and spreading around the country). There are also dialects in the Midlands, like Brummie (Birmingham). Smaller towns are,in many cases, losing their distintive features. I grew upin Leicester, which had its own dialect fifty years ago. Now it is harder to distinguish it from other towns in the area.
I can't give you a number, but it is very large. Oh, and welcome to UsingEnglish, Riz.