If you missed it, Radio 4's The World Tonight did a good programme from Chatham House last month looking at Defence. As I recall it, it featured General Wall, Lord Hennessy, Lord Robertson plus one more.
When asked what constituted the biggest threat to UK security they all said Putin etc apart from Lord Robertson who said our own complacency and refusal to take defence seriously.
An interesting listen if for no other reason than hearing what Lord Hennessy has to say which is always interesting:
http://www.bbc.co.uk/programmes/b055jslv