Sorted!

Thanks nacho for the advice. I called the US Guest Services and they confirmed that whatever the rate or how its paid I am as Platinum entitled to lounge access.

Within minutes the Hotel front desk Manager called and advised me the access key was waiting at the front desk.

I have to say the lady at Guest services was amazing!

Faith restored in Marriott....... YES, now if we could just get those lounges open at weekends!