whats the difference?

[ginger 69]

what is the difference between a visa electron debit card and a solo debit card? and why would a bank offer one but nut the other?

[fairy!]

Electron is Visa, Solo is Switch... banks generally offer you one or the other... like, I think all Barclays customers have Visa, whereas Halifax is Switch... (apologies if I'm wrong with these specific examples)

[Sammy Snake]

They are basically the same thing but run by two different companies.  As fairy! says, some banks offer one, other banks offer the other.  I don't think you will find any that offers both as they both do the same job so there is no point.

[stevie21]

I think some UK banks started to offer visa debit cards (and thus Electron cards) as visa is a more recognised brand in North America. This made it easier for UK customers (without having to rely on a credit card) to spend money with US shops/merchants. I'm guessing that this is a historical factor in a bank choosing Visa over Switch (and, therefore, Electron over Solo) but this is just a guess.
If you're choosing between the two, I'd try to find out if the shops that you'd normally use accept one more readily than the other as not everyone accepts both even though they both do exactly the same thing.