[UK] When is an email accepted as "In Writing"?

I almost never use snail-mail anymore and indeed, recently apparently accepted the terms of a new employment contract by returning an email with contract attached stating, as requested, "conditions accepted".

In the current situation I'm looking at this area

Access to Medical Reports Act 1988

which makes no mention of definitions of "In Writing".

Is an email to the medical assessment company denying consent sufficient, or should I revert to snail mail?