The link from Barton Road to the Lammas Land car park (and the car park itself) have been closed to all use by the County Council for some development work. This is a buisy cycle route, and no effort has been put into providing a diversion. Currently most people are cycling across the grass behind the hedge beside the road (though how long this will remain possible if it rains is unclear); an alternative is to use other paths across Lammas Land, but they are narrow, not actually marked for cycling, and it's further.
According to a notice at the junction with Barton Road this work will continue to the start of December. There was and is no warning when approaching from east of the river.