As there is a shortage of accessable lounges in TBIT, this could be very useful for UK based passengers with a late night flight back to the UK on Virgin, or other airlines.
On todays exchange rate, it would cost c£25 on top of the lounge visit rate, so at about £50, it is pretty decent value compared to the cost of food and a few drinks at other outlets in the terminal. Plus the ability to have a shower and change before flying home is priceless.
Obviously, if you have access to otehr lounges in the terminal your options may vary, but it seems a good offer for some passengers.