I would add another £10k easily for living costs, accommodation and beer money. You will be surprised just how expensive it can all be. Remember also that even best laid plans can change. You could for example head out to the US and find that what was meant to take x weeks takes y weeks through no fault of your own.
ATPL theory - you will need to go to Bristol for I think 2 weeks twice for the brush ups. A B&B is probably around £50 a night plus your dinner and lunch money. Will you drive there or fly down and taxi? For the exams at Gatwick will you be in a hotel or B&B? Then ditto. This really adds up. Also sign up for the Bristol database and its another £50 for 3 months access so maybe another £150 or so there.
Factor in for resits as well, particularly on the CPL and IR front. That is where the costs can really escalate. More so when you start getting into twin engine stuff and it is probably costing you the thick end of £300/hr to rent for a test. Then add on retest fees and it can soon add up to a very bad day.
Books and stuff - what is in the study pack you quote? Does it have the CRP5 that you will need for the ATPL exams? Does it have the Trevor Thom manuals to get you through the PPL exams? You might find that you need to buy extra books for topics like engines or MET. Most guys buy their own headsets as well. In the US expect to pay in US dollars what the price is in the UK. Probably another £150 or so for a decent set of David Clarkes unless you are feeling particularly wealthy and go for Sennheiser or something like that.