Harry investing £1000 in bank (5)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

I’m not sure I understand either the definition or the parsing here, so perhaps someone can improve on this. I can see HARRY might mean “ride”, be on top of, annoy, at a stretch and G could be a grand, £1000, and a ridge could (at another stretch) be a bank, but it’s weak.