Originally Posted by KARFA

You can get the airside bus to T4 and exit landside there. The buses start running down after about 8pm though. And obviously this won't work if you have bags to collect.

Otherwise, go landside at T5 and get the 482 or 490 TFL buses instead. You need to pay so oyster card or contactless card to tap in. Get off at the stop after T4, Starlight Way.