Hi Jonathan,
I was a customer of Barclays Premier, and then later Barclays Private Clients for about 3 years - previously I had a normal customer until I walked into a branch to complain about my credit limit on my card and after running through, they told me that 'someone would be in touch from Premier'. I visited their office in London and met the people that would be looking after my account - and the fee was £10/month.
Service was okay - found it useful to have named contacts and direct lines to call when I had questions. To be fair, I wasn't interested in some of the other wealth management options they offered so to me the only benefits were the posh cheque book, direct contact, and there was also the Barclays Premier Charge Card (this was in the days where AmEx wouldn't give me a card!) - which was £80, and was basically the top hidden tier of BarclayCard, had good travel insurance but you had to pay for the holiday on your card.
Alas the Premier Card has now been replaced -
http://www.barclayspremier.co.uk/ which has some benefits like standard Priority Pass and extended warranties on certain items you purchase.
Like I said they were okay, but I moved to Clydesdale Private Banking (
http://www.cbonline.co.uk/0,,40945,00.html) as they have an office onsite at my workplace, so I can drop it at anytime to pay in cheques or talk to my private banker.
Thanks,
Richard