At the end of last year, the companies revealed that they planned to work more closely together, providing obvious cost-saving benefits as the two come under increasing pressure from shareholders to save money while driving up average revenue per user (ARPU).
Telewest CEO Adam Singer said, "We will stop short of a merger of operations. It's not a precursor to a merger -- it's a precursor to both of us having to find ways of bringing scale without necessarily merging."
NTL and Telewest will work together in a number of areas, from purchasing digital cable modems and digital set-top boxes, to joint marketing initiatives to raise the profile of broadband cable.
They will work together in other areas as well, such as sharing customers in an attempt to reduce churn. The idea here is that when a customer moves out of one operator's franchise and into another, their package can be transferred without losing the customer to a rival such as Sky.
One of the most striking benefits of increased cooperation is that they would form a powerful force against rival platforms, particularly Sky, which is stealing market share from its competitors.
Sky has an in-built advantage over its rivals -- a powerful customer base. Sky has 5.3m subscribers compared with cable's 1.5m digital customers and digital terrestrial's 1.3m. BT is another competitor the two are watching closely.
This issue, coupled with the fact that NTL and Telewest do not compete against each other as their franchises cover different geographic areas of the UK, raises the issue as to why they do not go ahead, take the plunge, and merge.
Combined, they would present a serious force, offering cable's bundled service of telephony, TV and internet access. According to analysts, however, it is not that simple.
One drawback is the amount of debt each company carries. NTL's stands at around £10.9bn, while Telewest carries a burden of £4.8bn. As Singer pointed out at last year's Edinburgh Television Festival, both companies' financial positions "would made a merger difficult".
Above all, both companies still have a long way to go in rolling out their digital services right across the UK. This has taken longer than expected because of the sheer scale of the task of laying down the networks.
This was compounded last year when Telewest's set-top box supplier was hit by a shortage of components, delaying the rollout of its service still further.
NTL and Telewest are determined that the rollout of digital cable across the UK is their immediate priority. Once this has taken place and their financial positions improve, it is widely believed that in around five year's time a merger could take place.