Go the long way around, north of Scotland. Set speed to 7-8 kts and you will be able to get there & back with fuel to spare.
Oh, BTW....
Stay out of the CHANNEL
The Gib straight is not impassable because it is deep.
Even without changing your patrol grid, you can still make it in a VIIB.
Use your Nav Officer! Plot your course, set your speed, then ask the NO for a report on 'maximum distance at this speed'. Remember, you need to get back home.
