at LGW you can still get into the First lounge if you're flying domestic, and there's still a separate check-in queue for silver/gold cardholders for domestic flights - don't think either of those are an option at LHR T1
Unfortunately, the T1 First Class lounge is in International Departures, so travelling on a UK Domestic Flight you can only use the Domestic Terraces adjacent to Gate 5.
However, Silver/Golds and their One World equivalents (Sapphire/Emerald) CAN use the Zone R Premium Check In area to avoid the main terminal scrummage. However, you would have to go back into the main terminal to Zone East to enter the UK Departures security queue.