We can't always obtain or afford the .com variant of a name that we have fallen in love with for a major venture.
In these cases, the country code of the major countries is usually the best, followed by the .net. Your site and marketing strategy will then determine how detrimental not having the .com will be. Of course, once the site is success then you will get people naturally typing in the .com first, even when they have been to your site before.
Therefore, the biggest cause for concern here is that if the .com has the same business and business model as you then you will suffer at their hands. If you spent $25,000 on marketing hosting.net, for example, then hosting.com will get a few % of extra business.
If there is enough differentiation between the two then there is a lot less to worry about IMO.
To conclude, if I saw the .com and .co.uk (for me) was the same as my business offer then, even if the name was perfect, I would try and use an alternative .com instead of just accepting the .net or .org .