I have a new 15" MBP on order at £3300. I also have a similar spec XPS 15 which cost me £2600. So yes the MBP is £700. The XPS also has a better CPU (i9-8950HK) but that is kind of a waste, I only got it with that because Dell basically upgraded me to it for free.
However I have had no end of issues with my XPS 15. To the point that I have had enough and I am returning it for a refund and will pickup something else. The first unit had physical damage to the lid so I got a replacement sent. The replacement has coil whine, interference on audio out. backlight bleed and the space bar has developed a wobble so does not pick up all presses. For a £2600 that is unacceptable. I know people like to hate on the new MBP keyboards but I have not had a single problem with my 2016 MBP. That machine is basically perfect and I hope/expect the 2018 model to be the same.
To be honest I am fine with pay £700 more for a machine that doesn't develop a problem with the spacebar after 11 days as well as all the other problems I have had. If I were to calculate the amount of time I have spent on the phone with Dell and waiting around for collections/deliveries I doubt I would be far off that £700 in time waste to be honest.