If you're near the Westfield W12; the Bobbi Brown ladies in House of Fraser are really nice, as are the NARS ladies. BB counter staff spent 20 minutes trying to help me match a lipstick I'd seen in a magazine, even checking other counters for me!
I recommend the NARS tinted moisturiser and concealers. You won't get any pressure from the staff at HoF to buy on the day; they will colour match for you & write down the products used, if you say that you want to walk around with it on for a bit, see how it wears throughout the day, how it looks in natural light, etc. The NARS colour range is quite directional and I think you'd be best off moving over to Bobbi Brown for eyeshadows, lipstick, etc.
The other brand to take a look at is Clinique. If going to Westfield, stay away from their counter in Boots! They seem to be fresh out of training and go through the sales patter quite robotically, not really listening to what you're actually asking for. The assistant who I asked to colour match me to their foundation, applied it OVER the makeup I had on my face, then starting saying that my skin was flaky! No...You've caked makeup over makeup, that's why it looks shit.
The Debenhams Clinique counter is much better, assistants are experienced and have a more relaxed approach. Have a look at their Chubby Stick ranges for eyes and lips. You can go through the samples on the counter yourself, as you can with any counter where samples are on display. If the SA comes over, you don't have to accept their offer of help straightaway. I normally just say that I'm okay by myself for the moment, but I'll shout if I need them, then call them over if I want help working out which shade is going to work better, want one of the products applied on me to see how it looks, or I'm ready to buy something.
I think those are the only high-end brands I'd recommend for a new starter. Chanel, MAC, Benefit etc. are great for exciting colours and innovations, but I think if you can get your head around what products and colours are going to work for you with the help of the three brands mentioned above, you can start experimenting with the mid-range brands, without worrying about spending £17 on a lipstick, only to find you don't like it a week down the line.