Drivers rear shock broken MOT!!!!

My 03 Defender 90 TD5 has failed a pre MOT on the drivers rear shock no longer being attached to the body.... oops! Can I buy the shocks singly or should I get both replaced at the same time? Any advise much appreciated -another learning curve on shocks, already had the done clutch, PAS pump etc etc still I love my Landy I've looked online for parts, Island 4X4 do a cellular Dynamic Britpart shock for 28.33 +vat compared to mailorder 4X4 standard shock for £58.83 ... any recommendations??? Help!

Best to change both on the same axle even better to change all four if they are getting tired

Thanks, I;'' replace the back ones the noo and treat the Landy to new front shocks after the New Year. what about the cellular dynamic vs standard shocks? Cheers

i have cellular dynamic's fitted all round on my 90 had them on over 2years with no probs