Think I would struggle to invest a full £50k.
The things I would invest in / upgrade though are:-
Website - ~£3k - top of google for all the areas I'd like, not just my local town.
Equipment - ~£5k - 2 full sets of gardiners poles (including the 61ft supermax im probably going to have to buy soon)
Van - ~£12k - mines got 103k on the clock so it's going to need upgrading sooner or later.
Marketing - £10k - Would probably invest in an experienced telemarketer to chase more commercial work.
Apart from that I'm struggling. I'm happy with everything like my system, uniform etc.