I have to agree the RT fail Procedures don't seem to cater for this very situation, but i think th closest fit is para 3.2.4.1 (e) and (F)
http://www.ais.org.uk/aes/pubs/aip/pdf/enr/2010103.PDF
(e) On reaching the appropriate designated landing aid serving the destination aerodrome, begin further descent at the last
acknowledged EAT. If no EAT has been acknowledged, the descent should be started at the ETA calculated in (d) (i),
above, or as close as possible to this time. If necessary, remain within the holding pattern until the minimum holding level,
published for the facility, has been reached. The rate of descent in holding patterns should not be less than 500 ft per
minute. If 'Delay not determined' has been given, do not attempt to land at the destination aerodrome, divert to the alternate
destination specified in the current flight plan or another suitable airfield.
(f) Carry out the notified instrument approach procedure as specified for the designated navigational aid and, if possible, land
within 30 minutes of the EAT or the calculated ETA. When practical, pilots should take account of visual landing aids and
keep watch for instructions that may be issued by visual signals from the ground.
As for 'delay not determined', if they haven't said it then one isn't in that situation.