Speed increases are driven by competition in the market. Apart from a few fibre only providers in very selected areas, the fastest speeds achievable to the normal consumer in the UK are VM's.
VM is not competing with Ziggo, so why would there be any reason to match their speeds. VM Ireland speeds are not much faster (360Mb).
Cable customer since 1993. Services: FH TV, Sky Sports & Movies (2xV6), Talk Anytime Phone, VIVID 350, Virgin PAYG Mobile