I'm assuming this means I can just plead not guilty to the first charge of withholding the identity of the driver but guilty to the speeding charge?
Yes, that's the way to go.
Unfortunately different areas adopt different procedures, which makes it difficult to give consistent advice.
To be honest, the method you have been offered is far more sensible in most cases. The problem is, if you are not specifically told the offences are "in the alternative" and you plead guilty to speeding (which would not succeed without a guilty plea), there is a danger (admittedly a small one) that the court will then continue with the other charge and you do not have much by way of a defence to it. That's the reason why we usually make the recommendation as I did.
But not to worry - the method you have been offered seems fine.
