The new MBP is SOOO disappointing. I was waiting for it but I took the plunge the day before the announcement and I'm glad I did. I've been researching laptops for a week.
If you want a laptop that's basically the same as a MBP but more powerful I'd look at the Razer laptops. They have the ability further down the line to connect a GPU externally.
The laptop that you linked is very good for the price although they did have £100 off which run out 2 days ago which, would of made the base model £699. The only thing that put me off with that machine was the weight which I deemed quite heavy but I tend to use my laptop in bed on my knee.
The best laptops for £1000 or under with dedicated GPU are:
Razer Blade Stealth (graphics aren't amazing but can buy the external GPU at a later date)
Acer V5 Nitro
The dell you listed
Personally I decided I only wanted to spend as little as I could and bought an Acer Aspire here http://www.laptopsdirect.co.uk/acer-aspire-f5-573g-intelcore-i5-6200u-8gb-1tb-128gb-ssd-nvidia-gtx-950m-nx.gd6ek.002/version.asp I only paid £580 from Very as I made a new account which gave 10% off when using credit. I paid it off straight away with no interest