It's a Miami Monobloc Tap PVD Stainless Steel from B&Q.
You should be able to swivel the arm around the base part of the tap where the controls are but since it was installed it has always been stiff and when you move the swivel part, the whole tap (including the part under the surface of the sink) tends to move. The sink is stainless steel. I can't tighten it up any further so that the grip on the sink is better.
What can I use to lubricate the swivel part to make turning it easier? I was thinking of 3-IN-ONE Professional White Lithium Grease available here
Cheers,
Wes