9 days is manageable by almost anyone with a reasonable degree of fitness. 105 ish miles a day average which isn't as bad as it sounds. On the road at 9am, lunch at 12ish, afternoon cafe stop at 3ish, into next B&B at 5ish.
The Deloitte Ride Across Britain does it in 9 days and some of the people doing that were by no means regular or experienced cyclists.
The worst thing about it isn't the riding, it's the logistics.
Get down to LE on Friday, start on Saturday, finish on the following Sunday in JOG then drive down to Inverness for the night, drive back from there on Monday.
A support van/car is invaluable, especially if it can meet you at a pre-arranged point each day so you can drop off excess kit or pick up waterproofs etc.
My personal opinion is to run each day as it comes rather than to rely on a pre-arranged destination. That way if you're having a bad day and you're way behind schedule, you don't need to push on to get to [location], equally, if it's good weather/tailwind, you can probably go 30 miles further than planned. Get to 3pm, call your support crew, tell them you'll be at [location] in 2hrs, get them to find a B&B/YHA/hotel and book it for you.