I suggest you do it just to see if it works.
Tried it, no change. Still getting a partial connection (so the PC can connect to the VPN endpoint) then "Failed to update policy" which halts the connection. It's the policy update port that has been blocked in the latest firmware according to my company's service desk, and port forwarding etc make no difference.
You appear to be suffering one of the problems of using a residential broadband service for Business use that is why BT operate a Business service for and you would get the support there you need
I'd hardly say connecting a work VPN is 'Business Use'. Perhaps if you were running a buisness that depended on the line (i.e. you were running the VPN server) the I'd constitute is as such.
It's not a valid excuse anyway. I run a VPN server at home which I've been unable to connect to since I got the Home Hub 5 since it blocks inbound GRE packets - I use the VPN to stream music and videos to devices when I'm away from home - am I expected to fork up the extra money for a business line to get this to work?
Simply fact is BT treat us all like idiots and lock the box down so tight that its unusable for anything except WWW traffic. The OP's problem is clearly caused by a FW change made in the latest firmware of the box and shows craptacular UAT from BT.