The Heathrow Airport Loop is the perfect setting for a high-tempo time trial with a relatively unimpeded flat loop around the airport.
The Reigate Hill Gravel Loop follows a clockwise circuit to Reigate Hill and then south of Box Hill before returning to London.
The Panshanger Park Loop cycling route heads up through North London via the Swains Lane climb in Highgate, and this time heads towards Hertford. After the café stop, the route loops around Panshanger Park before the southerly leg heads back to Regents Park via Hampstead Heath.
Following the same alternative route out of London as the Bayley Hill Loop but this time going on to Shoreham for a wider circuit back to London.
The Wendover Loop cycling route takes a steady climb out of West London, leaving London north of Uxbridge before heading into the heart of the Chilterns.
If speed endurance is what you are looking to build, Drift Road offers a long flat straight.