DTCI getting a taxi staying at Park Inn the night before

I need some help please......

I am staying at the Park Inn Heathrow the night before I fly to Chicago. I want to do DTCI so need to get a taxi/car from hotel in the morning. I want to make the most if the Clubhouse so would be picked up before 7am which is the time the phone lines open to ring through reg number etc. so I would need to know the details the day before. I have priced Tristar but I cannot justify laying that price for such a short journey. Does anyone know of a local company that could confirm the drivers name, reg no etc the day before or any suggestions on the best way to go with this. I have never tried DTCI and I sooo want to .

When I did DTCI I stayed at the crowne plaza, the concierge arranged it all for me. They phoned me with the reg. could you ask the concierge to give you a taxi firm number and call them?

Thanks
Sounds like a good idea. I did think maybe the concierge might be the best route to go