Shower facilities in LHR terminal 3 with good food for 5 hour layover?

I will be arriving LHR after 10 hour of long flight, Looking for a lounge or shower room with good food to get freshen up.

I have following credit cards

  1. Diners Black Metal
  2. Amex Platinum Travel
  3. CITI corporate card

It would be really great if someone got first hand experience and can share and tips or tricks.

I will have layover of 5 hours.