PD 5500 is NOT a standard but a published document and has been replaced by EN 13445 for PV design and construction.
PD 5500 5.6.6.2. Ultrasonic techniques references BS 3923 Part 1 whereas Part 3 is for automatic UT. The TOFD method is covered by BS EN 583-6. Phased array methods are used in PV construction inspection also being treated as similar to conventional UT.