re: 5 miles from the centre of Cambridge in a brand-new development
Be interesting to know the key details of the BT Openreach telecomms installation that covers your development (ie. street cabinet to home) to see if BT really are planning ahead for FTTP and are either installing tubes for blown fibre or an actual fibre tail to each home. Informally, you may be able to speak to the BT guys when they open up the man holes or simply investigate the duct entering your house, but for the definitive answer just ask the developer.
I suspect you (and your neighbours) may have grounds for legal complaint, if relevant parts of your development were planned after the announcement in 2010 of the UK broadband project and commitment to an absolute minimum of 2Mb in new build...
As for digging up roads, I've noticed that various utilities are increasingly using cable moles.