This is in-line with both EU and International harmonised spectrum policy.
The 700MHz band is already used for wireless broadband in countries such as North America and the EU also wishes to move in this direction to cope with future broadband spectrum requirements (the band could be used for LTE or other wireless broadband technologies). The 800MHz band is already being freed (as part of the digital switchover) and is being auctioned in early December 2012 and should be available in March 2013 and it is assumed the licensees will operate LTE services in the 2 bands being auctioned.
In order to move DTT services, it will be necessary to ensure maximum spectral efficiency and thus it's likely DTT MUX's will all have to migrate to DVB-T2 and MPEG-4 (as is used by Freeview HD) which may affect end-users as they will have to ensure they have the correct systems to receive these transmissions.
Ofcom are also keen to promote innovative new services such as White Space Devices (WSD) as these can use parts of the spectrum that aren't being used for DTT services (this is mainly due to overlapping DTT regions that have to use different frequency sets and thus there are areas of spectrum that are left empty in one area so as not to interfere with neighbouring areas). The 'white spaces' are perfectly usable for controlled transmissions that wont interfere with neighbouring areas, but can provide spectrum for broadband. WSDs will need to contact a central database, both to ensure that they are only using allowable frequencies and also Ofcom may enforce a kill switch to ensure that if interference does occur, that the devices can be remotely disabled.
Currently trials of WSDs are taking place in the 700MHz band.
Though 2018 seems a long way away, it took a huge amount of effort to ensure the current digital switchover could take place and it seems that this is really a second digital switchover (though DTT services already operate in the lower 600MHz band so new equipment and transmitters/etc shouldn't be required).