Hopefully, I'll make it all the way! 
Given the rate at which you say it's leaking I'd be VERY cautious ..
You MUST keep a VERY careful eye on the temperature guage and stop as soon as it starts to climb, or you risk much more damage.
Once you stop DO NOT just open the header tank to top up, this will drop the pressure rapidly causing the water to boil. This is DANGEROUS to YOU, and can cause more damage. Wait at least 30 minutes for the thing to cool down before topping up.
Do NOT use motorways as it is difficult/dangerous to stop and top up water on the hard shoulder.
Obviously you will have to carry quite a lot of spare water, make sure you have florescent jacket as well to wear whilst outside the car.
Allow LOTS of time and take a good book to read while things cool down. Ensure your mobile is fully charged and handy.
I would advise against travelling alone.
Sorry to be such a "wet blanket" .. but your safety must be a concern. You are driving a "problem" car .. please don't make the problems worse by not preparing for the journey.
I go with the drive a short distance - call Green Flag option ...
