I phoned up a Toyota garage before buying my 86 (2016 plate at 53k miles) to ask them about this service because I wanted to use it as a bargaining tool to get more money off when buying the car.
When I phoned up the garage they informed me the spark plug service is now standardised as part of the standard price service of £395. Of course, that's just one guy on the phone and could be wrong, but I hope he isn't...