Yes, both T3 and T5 have Hermes boutiques. I transited through in December and it was the cheapest place to purchase Hermes...Even cheaper than France with VAT refund!
If you have a long layover you can utilize the personal shopping service and they can assist you with shopping at both terminals.
I have seen a plethora of bags including roulis, halzan, Evelyne, leather Garden party tpm, Jige, egee, double sens even Constance 24 and 18 but have not seen a Lindy the past three times I was at LHR. There's always goodies in the back just ask the SA if you get a good vibe with them and they will be willing to recite the inventory in the back.
Pricing example: 32 MM belt kit with gold Guilloche buckle and Epsom/Chamonix strap was $627.90 (when currency was converted) compared to the US price with sales tax of $952.60.
All leather garden party was under $2,100.
God bless that duty free pricing and favorable exchange rate!
If they do have a constance at the airport, would it on display? or do you have to ask and the SA will answer according to if he/she likes you or not? thanks.