Fuggles & Mosaic? Yep, definitely - it's a mix I have tried (with Citra & Amarillo) with success.
But.... Get yourself a really clean, bittering hop (Warrior?)
You'll only need about 20g for a 25l brew - if you don't chill, then 15g is plenty. Use this for bittering - you won't waste your aroma hops.
How malty & how strong do you want your beer?
Try 4300g M Otter & 500g Crystal in your mash.
Boil wort for 60 mins with the Warrior, add 100g Fuggles at flameout. Keep the Fuggles in there for at least an hour (overnight, for me with my no-chill method). Ferment in a primary FV for 5-7 days. Krausen should have died down a lot after this. Only at this stage add your Mosaic, as dry hops. How much do like like a hoppy aroma? If a lot, add at least 66g Mosaic. 100g is getting really serious!
Well, that's what I'd do - many other ways to go about it!!! :)