Southeastern services from Paddock Wood, Tonbridge and Hildenbrough serve London Bridge, London Waterloo East and London Charing Cross. There are also direct rush hour services to London Cannon Street. All these stations are directly on the London Underground network and served by extensive bus services. For full details of travel in London, including an online journey planner, see the Transport for London website.
Always remember that it's often easier to walk than to get the Underground for short distances. Also, the best journey may not always be the most obvious one. For example, passengers from Tonbridge to Canary Wharf may find it easier to change at Waterloo East rather than London Bridge, because the connection on to the Jubilee line at Waterloo East is much easier - just follow the signs on the platform to Southwark station. Also note that Charing Cross is as close to Embankment tube station as it is to Charing Cross tube station itself!