It depends what day of the week you are travelling.
There will be a mixture of old and new planes - from memory, the A330s were due to fly Ex-LGW Sat Sun and Mon - not sure if that is still current though.
If you do a dummy booking and then click on the red flight number(VS049 for example) on the page that has the dats/prices and flight options that will tell you the type of plane scheduled to do that route on that date.