FlyerTalk Evangelist
Join Date: Oct 2001
Location: Falkirk, Scotland,VS Red, BA Gold, HH Diamond,UK Amex Plat
Programs: Master of the Privy Purse des Muccis
Posts: 18,078
Hi,
Details of the HEX service here;
https://www.heathrowexpress.com/engineeringwork.asp?SID={B16FAC68-1FEE-4706-888A-B0568133B392}&SUID=410&type=0
It is a bus with last service leaving paddington at 2010. ( although the railway takes 20mins or so I would allow lots of extra time for the bus journey)
As uncledude said, you can only use T4 Gate 1 combined lounge and you will not be able to access T5.
Welcome to flyertalk and the BA forum!^
Regards
TBS