I don't think that's right.
Even the government website makes the point there isn't statutory entitlement to time off.
"This bank holiday will operate in the same way as other bank holidays, and there is no statutory entitlement to time off. Employers may include bank holidays as part of a worker’s leave entitlement."
Also my example was specifically not 'X Days + BHs', it was 'X Days Inc BHs', subtle but important difference when it comes to contractual leave entitlements.
I wouldn't assume all employers will be dishing out an extra day off, it'll be dependent on your contract and depending on what that says, their discretion.