new bike advise pls

If i have this amount of money, i would prefer something custom! What better from a bike build especially for you and your needs and quality*****.

I'm not going to advise you on a bike, but, particularly for that money,  I will advise you to go to a local bike shop that takes an interest in you and will fit the bike to your needs.  Want a bigger cassette sir, no problem, narrower/wider bars, firmer/softer saddle, done, tyres changed etc etc.  If you can get a formal bike fit included for the price, so much the better.

could probably get a bike with a proper headset for that money

"I'd actively avoid the mainstream brands and get something made in the UK or Europe by someone who really knows what they're about."

Can you explain what that sentence actually means?

Yeah what nadsta said.

I'd spend the 6K like this

Canyon Aeroad CF SLX 8.0 Di2

Tacx Neo

Some cross bike under a grand on eBay

Zwift subscription

Picked the Aeroad as objectively it seems to be the best bike in the world in terms of stiffness/weight/aerodynamics according to Tour testing though the Foil is also scored very high. Use the crappy bike on the trainer for intervals and for wet rides.  

If this is to be your only bike I would seriously consider splitting your budget approx £4k/£2k and get a summer and winter ride.

New disc aeroroad just reviewed here seems like a good place to start, with a disc endurance bike for crap weather. (BTW I am not a Canuon fanboy or owner)

Slightly off topic, Ive just read a piece about the Specialised Venge, where they are trying to attribute significant speed and time gains down to the bike, but in reality its the fact the comparison was between a bike with standard wheels and non aero clothing and a bike with 60mm rims and a rider in a skin suit. 

Just got to love sales promotions!

Advantage of going to the bike show is that you will get to see lots of bikes from smaller brands that you might not know about, and you will be able to talk to the people from those brands.  With the sort of budget you have you could get a top quality bike from any of the major brands or something really special from one of the smaller one, or something that is custom.

Have a think about what you really want from the bike and how you are going to be using it. Keep that at the front of any conversations with the brands.

Many of the brands will have bikes to try out at the show - take fully advantage

With a £6k budget, buy all the bits yourself and save £2k. Or build a one off special with all bells and whistles for £6k

You should also visit a few dealers, as shiny stuff on show stands isn't a good way to make such an important purchase.  And don't close your mind completely to other options, sometimes a model you'd not considered ends up being 'the one'.

Most importantly, don't believe the hype. Buy the bike you feel happiest with, preferably from a dealer that provides excellent customer service.