Is this correct? I thought disabled badges can be used in any parking bay.
No, for instance you cannot park a car with a blue badge in a motorcycle bay or a bay for buses only, regulation 6 of The Local Authorities' Traffic Orders (Exemptions for Disabled Persons) (England) Regulations 2000 (https://www.legislation.gov.uk/uksi/2000/683/regulation/6/made) says (my bold):
6.—(1) The following provisions of these Regulations have effect for requiring local authorities to include, in orders to which these Regulations apply, exemptions in favour of a vehicle displaying a disabled person’s badge.
(2) Any exemption from a provision which these Regulations require to be included in an order may be limited to vehicles of the same class as those to which the provision applies.
I couldn't tell you off the top of my head whether an electric vehicle is a "class" within the meaning of the legislation, but I suspect it probably is. We obviously don't know what the traffic order says, but given the wording in 6(2) it is entirely possible that the traffic order prohibits blue badge holders from parking non-electric vehicles in the bay.
What is rather curious is that, on the face of it, a blue badge holder could park an electric vehicle in an electric vehicle charging bay without actually charging and without time limit, or at least that appears to be the case given the regulations do not appear to have ever been amended.