Still in budget territory at £150 unless you look 2nd hand. I've got the Monitor Audio Bronze B2s (£180) and while they're definitely better than the Eltax Monitor 3s (which I also own), I wouldn't say they're massively better. I've also owned the Wharfedale 9.1s, and again not massively better than the Monitor 3's, and not better than the MAs either IMO.
I think you need to spend more and possibly consider 2nd hand to get a really significant upgrade. I've heard more knowledgeable people than me say often that you need to spend 5x what your current equipment cost to get a genuine upgrade. Dunno if that's exactly true.
I should also say that while the Monitor 3's aren't the most sophisticated speakers around, they are clear and don't overly colour the sound. And they're cheap now because they've been around a long time and are heavily discounted, but they were originally sold at £150, so you're not necessarily getting better quality by buying something else for £150 now.
Something to look at - 2nd hand B&W DM601s maybe? (not too old)