I think you maybe under estimating just how much this will cost to run.
It's going to be a false economy if you are only going to do 'one or two' nights/days with it.

I have a hand in the Hackney cab trade and whilst I appreciate its not the same thing, if you are 'plying for trade' (advertising for airport runs) you will need the relevant public carriage insurance for a start (for my black cab its £2000 per year - just to give you an idea)

You will also, as far as i am aware, need the vehicle to pass the council test (which is done twice a year at £500 a pop depending on the council authority) to ensure its road worthyness complies with the relevant hire legislation

Dont want to put you off and I wish you the very best of British luck, but your best to contact the council and research all the relavent licences and insurances that you will need to have.

you could ignore that advice and do it 'underhand', but the moment you have an accident on a job and your passengers are hurt you will be fucked big time.

Oh there is one type of vehicle that I see round Manchester as 'executive' hire vehicles that no one here has mentioned and it would suit your needs perfectly if you go ahead:

The Mercedes V class (think its now the Viano). they do it as an 'executive' 5/6 seater people carrier with privacy glass and all the bells and whistles.
This will be more suitable as it'll have plenty of space for luggage and be perfect for Airport runs. They can come with full leather and swivilling seats if your 'clients' are business people having a 'pre business' meeting en route to a venue ect.

Good luck!