Everyone, thanks for your assistance. Having had a hunt around on the web, I discovered the article below which explains things in the UK pretty clearly. The repeaters here do transmit with a CTCSS code, which is not as I had thought, but only when in talk through. That was what I had missed out on....my mistake. So, now I know.
CTCSS on the Repeaters.
CTCSS- Continuous Tone Controlled Squelch System- is now used on most UK repeaters.
The system is used in addition to the conventional 1750Hz toneburst access system, not as a substitute, its use is at the discretion of each Repeater Group, except on 6 metres, where it is compulsory.
The official RMG specification for CTCSS is:-
There is no need for any groups to fit CTCSS to their repeaters, but if they wish to do so they must adhere to the RMC plan which is based on geographic areas (see below)
CTCSS when available is in addition to the standard 1750Hz toneburst access NOT a substitute.
The current standard remains unchanged. It expects a normal receiver sensitivity of 0.3µV
In practice, this means that a signal of about 0.6µV is required to open the squelch which usually has a 6dB hysteresis. However when the repeater's receiver detects its own CTCSS sub-tone, the squelch can open at a lower level, providing a better service for those equipped to take advantage of it, while not affecting the service to others.
The repeater has to radiate the same sub-tone but only when it is in talkthrough. Thus stations which monitor the repeater with receivers using CTCSS need not hear the regular morse identification.
Where a repeater is fitted with CTCSS it must identify the sub-tone used by appending a word gap (7 dot spaces) and then the sub-tone identification letter to its morse identification so that all users are made aware of the sub-tone required.
The recommended deviation for the CTCSS tone where used shall be 500Hz ± 200Hz
Nine different sub-tone frequencies are allocated for UK repeater use:-
Tone A = 67.0Hz
Tone B = 71.9Hz Tone C = 77.0Hz
Tone D = 82.5Hz Tone E = 88.5Hz Tone F = 94.8Hz
Tone G = 103.5Hz Tone H = 110.9Hz Tone J = 118.8Hz
I hope this has proved of some interest. I now know how to access the 6m repeaters, which was the reason for my question.
73's Andy. 2E0WBL