Alex - good points about my post. I was still knackered from a 14 hour shift the previous day!
To correct:
If Vmcg is greater then V1 we dont take off.
On hot days, high humidity, high altitude take off, low weight we need to check what our actual Vmcg is. If V1 is greater, we reduce V1 to Vmcg.
V1 must never exceed VR.
In practical terms - on Sunday when it was 38 degrees just down the road in Kent from Southend Airport. If you were positioning a 757 that had just had a respray at Southend on to Gatwick you would be very wise to take a careful look at your performance figures - short runway, light weight, hot day, high humidity.
Not so tired now.