Presumably, you're looking for something like this:
Note: if you use an active DBMS like SQL Server, there are simpler variants than a subselect.
SQL:
SELECT
V.ID AS VehicleID,
T.DateVal AS TripDate,
V.REGN_No,
T.ID AS TripID,
T.Place_Travelled,
(
Select Top 1 X.Fuel_Closing
from Trips as X
where X.Vehicle = T.Vehicle and X.Fuel_Closing < T.Fuel_Closing
Order by Fuel_Closing desc
) AS Trip_Opening,
T.Fuel_Closing AS Trip_Closing
FROM
Vehicles as V
INNER JOIN
Trips as T ON T.Vehicle = V.ID
ORDER BY
V.ID, T.DateVal, T.ID
Note: if you use an active DBMS like SQL Server, there are simpler variants than a subselect.