Looking for more information I found the Amphibian and Reptile Conservation site (http://www.arc-trust.org/animals/common_toad.php) that suggests that toads like deeper water so maybe they were heading for one of the lakes either the reserve lake or one of the 3Ts lakes next door.
For more information about frogs and toads and making your own ponds the Oxford based national charity Pond Conservation (http://www.pondconservation.org.uk/) has a wealth of information. This organisation has a mission to create 30,000 new ponds by 2020 to help to redress the massive loss in ponds during the last century. They have been instrumental in helping the LWVP create several new ponds in the Lower Windrush Valley at Standlake Common and Rushy Common Nature Reserves and also in Witney Lake Country Park. These ponds are already providing good habitat to a wealth of plant and animal species, some of which are quite rare.