Correct. You wind up with a new and very direct competitor where there wasn't one before.
World before .uk: .co.uk is undisputed king of the hill
World after .uk: who knows which of .uk or .co.uk will win in the long run, either way there's a battle going on
So you are "losing" the opportunity to ensure you win the .uk/.co.uk battle regardless of outcome by securing both domains.
I don't think there would be any real competition after a few years.
It seems inevitable that .uk will take over as it is simply shorter:
Easier to brand, easier to type and easier to say by two syllables.
As soon as big companies start dropping the '.co', then everyone will follow.
If Nominet were being sensible about it and automatically gave all existing .co.uk registrants first rights to the new domain, then I don't think there would be very many objections.
But even although the current release is flawed, most .co.uk name holders now have the opportunity to 'upgrade' their domains.
I have had similar .com and co.uk domains, and the amount of direct type-ins on the .co.uk names were minimal compared to the dot com, even when comparing to US traffic alone.
By population size the UK is around 60m compared to 300m
Yet direct type-ins are far less than 1/5 as much.
This proves to me, that for many people, the .co.uk address is just too much bother to speculatively type in.
Current selling prices also reflect this.
I figure most sites will have moved to the .uk within 2 or 3 years, use their existing domains to forward traffic and emails, then probably just let them drop after 5 years or so. They will be ancient history by then.
So there are going to be additional costs for a couple of years, specially for domainers with large portfolios.
But I think this is far outweighed by the higher values that will be attached to the direct.uk names - I would guess they will sell for at least twice as much.