I'd agree with South - never been able to get a quote from a broker that was lower than what I could negotiate myself. Like South, I am also on a rate that is much lower than the advertised rate for the type of mortgage I have. Negotiated it directly face to face with bank. I dont want to go into any of my personal financial details, but it is not a discounted or any other sort of special offer mortgage where the rate goes up after the special offer period. It is a straight forward regular tracker at a set percentage above ECB for the duration of the mortgage - though the percentage is lower than advertised.
Brokers tend to be quoted the advertised rates and may be good at sifting through those rates. However, some banks are always willing to do a deal so long as they are still in profit overall. Bank Managers individual branches still have some power to offer lower rates on any product they are offering in order to retain valuable long term customers.
I dont think everyone gets the same treatment and I think it varies from branch to branch even within a chain. People who are not long term customers with good credit ratings will not get favours. Also, individual branches who are struggling with profit margins wont do favours.