I find five years to be very unrealistic. Where is the scientific proof that a contemporary aramid belt will significantly deteriorate in such a short amount of time? If VAG UK is the only organization in the world offering this advice, it strikes me as a shameful instance of making money off of unneeded labor.
The little unenclosed fan belt that also powers the alternator on my TR7 is still functional after 43 years. When the vehicle was dismantled after 21 years and more than 160,000 miles, the original Focus OEM cambelt was also still fully operational. Cheapo cambelt repairs carry the danger of replacing an excellent original belt with a subpar one from who knows where and improper reassembly of the apparatus by a cack-handed technician resulting in misaligned timing difficulties reducing power and increasing fuel consumption...or worse.