Hi matfactor,

I have some info for you.

A high quality concrete artisan will make a mix that is so dense waterproofing should not be an issue. But there are chemicals that can be added into the mix that will make concrete completely waterproof. Unless one is casting a holding tank or a fountain a sealer is more than sufficient.

Metal effects can be achieved a number of ways.
The most common would be to add metal pigment to a wax or sealer. You can control the level of translucence or opacity by the percentage of metal pigment. I've attached a photo of one of our sinks with a copper pigment at heavy load rate into a clear sealer.
Another option is to use one of the cold flow metal products available. These are real metal flakes in a clear suspension that are sprayed onto the surface. Since these are real metals they will oxidize. To stop the natural patina a sealer can be applied.

I don't know of any high performance concrete fabricators in the UK but I know there have to be some. My favorite GFRC (glass fiber reinforced concrete) gun is manufactured by a company about two hours away from you in Bristol. I will paste a link to their website. I would call them for a referral.
http://www.power-sprays.com/gfrc-equipment/gfrc-spray-guns/

One of the cold flow metal manufacturers also happens to be near you. They are a little over half way to Bristol in Hungerford. In addition to applying the metal coatings they also offer training and products.
http://www.metall-fx.co.uk/

Regards,
Vincent Cathcart
VC Studio Inc.
vince@vcstudioinc.com

Thanks VIncent - much appreciated...Matt