The relevant legislation in the UK is thus:
2.2.1 Breaks in Operational Duty
2.2.1.1 No operational duty shall exceed a period of two hours without there being taken during, or at the end of, that period a break or breaks totalling not less than 30 minutes.
2.2.1.2 At units where workload for any part of the day is judged to be low and the activity is spasmodic rather than continuous, periods of operational duty, at these times, may be extended to a maximum of four hours, provided that the following break is taken pro-rata (e.g. 45 minutes after 3 hours or 60 minutes after 4 hours). (see Note below)
NOTE: Judgements on unit workload are to be made by unit managers in consultation with the appropriate Regional Manager of ATS Safety Regulation in the case of Airports or the Head of En-route and College Regulation in the case of Area Control Centres.
In NATS, the union have also negotiated enhanced relief for various busy operational positions at various units and various times, bringing the maximum working time down to 1.5 hours. Note that this is not a legal maximum, which remains at 2 hours, but an acceptance by management that 2 hours providing an ATC service is not sustainable in the interests of fatigue and safety when faced with busy and complex traffic patterns.
The IAA fellow who spent time at NATS must have seen this in practice, or been briefed on it. Unless he walked around with blinkers on, or never actually set foot on a busy NATS unit.