Don't launch mass registration in the second level. It was sensible for it to have been protected from mass registration for all this time because it allows further third level extensions to be created if required. In 2004 me.uk was one of those. and people use it. We don't and cannot ever know what we might need to create at the third level in the future. Protecting it is sensible.
Brazil, a country with a population of ~200 million people, and one of the large emerging economies protects its second level. A list of all their third level extensions (use Google Translate to translate Portuguese to English) can be found at:
http://registro.br/dominio/dpn.html.
If we need further business orientated extensions under .uk then consider them in the third level. An obvious one is .com.uk which is reserved and could be offered. I wouldn't expect this to usurp .co.uk and it wouldn't block out the possibility of future third level extensions. If I had to choose between opening .uk or .com.uk to increase the availability of domain names to be used for business I'd pick the latter without hesitation for the reasons already explained.