The 1007 isn't a significant upgrade from the Forum, but it's easily worth £300 in the condition you describe. If I had £150 going spare, I'd take it as a 'project kit' or a gigging kit and modify it or something similar. If the cymbals are any significant brand name, you could sell those and make most of the money back.
The 1007 series has very solid build quality and decent shells. They're not high-end by any means, but they're a very good kit and one of the best 'basic' kits on the market. I have recommended the even-lower end 507 series before as a low end kit and the 1007 is an upgrade from there. For £150, I'd be all over it. I do think the Sonor kit is better than the Pearl. Both have decent shells, but the Sonor has more practical hardware.