It sounds like you are already doing what you can on the keyword front. So there comes a point where you can’t do any more with the terms. So then you move on to audiences, if you are already using those and adjusting bids accordingly. You have the device bids, locations, as schedule you can also work on. You can try to “prequalify” with ad text (for example “loans from £2000) but you will always get users that click without really reading. On a keyword as broad as that to be honest you are always going to have issues. Personally I would be looking at data in regards to lead quality by creating different conversions. Ie low, medium, high quality leads and then optimise based on THAT data instead.