OK, assuming your two pockets are each approx 3 inches wide and 6 inches deep, and can be filled to abut 3 inches without bursting (although you'll look very strange if they are trouser pockets !)... that's 0.03125 cu ft per pocket, so 0.0625 cu ft per trip.
Using Rhakios' figures, your 4 tons of pebbles will have a volume of 80 cu ft. Which means you'll have to make 1280 trips to get your 4 tons of pebbles.
Not knowing where in Surrey you are, I don't know how long each trip would take, but assuming you won't make more than one trip per day that's 1280 days... if you work during the week, that would mean 640 weekends, or in excess of 12 years.
Then add up the costs of 1280 day trips to Brighton...
... if I were you I'd just go buy the pebbles from Rhakios