It was £24.3 billion, and more importantly, they didn't invest, they bought it out taking advantage of the currency devaluation. They made 5 year commitments in terms of workforce numbers and the company HQ remaining in the UK, but what happens after that? Even immediately SoftBank are now free to move ARM's IP & lisencing revenue where ever they like.
That wasn't really a giant investment though, it's the standard the re-tooling costs for the existing Sunderland plant to set them up for production of the next gen Qashqai and X-Trail models. Staffing levels will remain unchanged, and they only agreed after the UK government agreed to absorb all levies imposed on their exports, which could be up to 10% if they fail to agree trade deals as is looking increasingly likely. Those same assurances are being given to other UK manufactures who export ~80% of total production. Could be expensive.
My bad for getting the Arm takeover figure wrong but the rest of your post is hilarious.
In both those cases if the investment hadn't happened you would be declaring that as evidence the Brexit vote is harming the UK.
All the economic data so far has confounded every single warning of doom issued before the vote.
http://news.sky.com/story/business-investment-helps-uk-growth-stay-firm-after-brexit-vote-10671206