take a look around Timezone.com, Watchuseek, watchprosite, the watch forum, PMWF, TZ-UK
Online dealers look at Blowers, and Chronomaster both have excellent reputations.
What is it you are after?
Dress
Divers/sporty
Pilot
Chrono
£1500 is a funny price bracket for second hand - there is not much around, plenty of stuff higher and lower.
look at
Anonimo - offshoot from Panerai
Ball - brand new (tritium tubes as lume which is interesting) I like their big pilot watch and the Hydrocarbon range.
Oris - some really good 'dive/sport' and brand new in your bracket. Carlos Costa, and the regul;ator are my fave's
Sinn
Nomos
Plenty of sub lookylikes with good quality movments and sapphire crystal from people like Marcelllo C, Grovana, Debaufre etc and all <500 so you can add another to the collection
Zenith - Rainbow flyback with the allegedly best chrono movement ever made 'El Primero'
Corum - Admirals cup range
Chopard Mille Miglia - nice
WatchUseek are full of small ateliers chucking out phenominal quality pieces in small numbers - unique rather the common as muck rolex and omega's
just look around the sites.
just to name a few