You don't haven to present yourself at check in, if your his and has the allowance for enough bags for the two of you. Which will be th case if you only have one bag.
If you check in online and have a online or mobile BP you just need to turn up at the gate in time or meet conformance, if that exists at LGW, at Flight Connections or security.

They won't ask where you are when your husband is at the desk, I have done that before, so don't worry about not being at the desk. And if they do, your husband just tells the truth: "She transferred through Flight Connections". You are not doing anything illegal here.
But you must have checked in before turning up at the Gate, otherwise you will be a no show and you will also need a Boradng Pass Tp get through Flight Connections.

I can't comment on documentation issues for the UK but make sure you check this out before you travel, to avoid any nasty surprises.