Virgin Money Travel Insurance [closed]

Most likely this is for the legal reasons, at least in US (and I am speculating that UK is similar on that matter).

The insurer typically requires the claim form to be signed by the insured (or beneficiary) to start the claim process. This signature has important legal consequences - for example the claim has to be processed under certain period. And you are legally responsible to provide truthful information - this includes other documents, such as bank statements, which support the claim amount. So someone who just sold you the policy cannot do this for you, even if they got the copies.

It is also in your best interest to work directly with the insurer (which I assume is InsureAndGo). Adding someone into the intermediate loop increases the chance some paperwork would get lost in mail, and this would make it much more difficult to track it. And handling insurance is annoying enough even without this.