After graduation the standard full time training pathway is:
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FY1 (foundation year 1), 3 rotations of 4 months each (usually in the same hospital). Theoretically an FY1 could be called a "JHO" (junior house officer), but no one does ever.
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FY2, 3 more rotations of 4 months each (usually in the same hospital, usually a different hospital to FY1 though). FY2s are the first/lowliest "SHO" (senior house officer) grade.
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Enter either a "core" training or run through training programme. These are called "core training" or "specialty training" or "GP speciality training" so eg in the first year of these programmes you would be known as CT1/ST1/GPST1, in the 2nd year CT2/ST2 etc. At this stage you remain an SHO. Core programmes end after 2-3 years then you apply for a further higher specialty training programme, run through programmes the 2 are joined together effectively and you just apply at the start after completing foundation. During this time rotations are usually 6-12 months, more often 6 months. Not usually at the same hospital.
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Become a registrar (also shorthanded to "SpR" for Specialist Registrar) - (happens automatically with progression in a run through training programme, or if you have finished a core training programme you will have gone through a further application as above). This tends to be everyone who's badge says ST3-ST4 and above. Registrars are quite senior doctors "on the shop floor" who in some specialties might lead a resuscitation or might carry out surgeries independently etc. Usually rotations are 6-12 months, not usually at the same hospital.
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Consultant.
Training lasts a really variable length of time depending on specialty, so eg GPs are a registrar for 1 year (ST3) after being an SHO for 3 years (FY2/ST1/2), paediatricians are typically a registrar for 5 years (ST4/5/6/7/8) after being an SHO for 3 years (FY2/ST1/2).
Some programmes you keep very much to your specialty (eg once in surgery you won't do medical rotations, once in paediatrics you won't do adult rotations) even during SHO years. In others (particularly GP training), you do a mish mash of different specialties during SHO years. Registrars are generally only within their destination specialty though (including GPs hence the "GP registrar" at your local surgery).
In your local ED department the registrars will be emergency medicine trainees working toward EM consultant, possibly some anaesthetics trainees (? Not totally sure), and staff grades not in training (who may have worked in EM a very long time). The SHOs will be a mix of FY2, GPSTs, and STs from EM and anaesthetics (they share a core training pathway). Plus doctors from other specialties (medical, surgical, obstetrics, paediatrics etc) will visit to see their own specialty patients, sometimes planned via GP and sometimes on request from the emergency dept doctors. There are a lot of junior doctors working there, most of whom rotate hospital every 6-12 months, so it's no wonder you may not see the same one twice!
Additional to this doctors often also take years out of training or between programmes to do things like clinical fellowships, extra qualifications, research etc.
All doctors below consultant are called "juniors" even though quite a lot of them are actually very senior / experienced. It can take 10-15 years from graduation to become a consultant and not every doctor chooses to become a consultant. Some will leave training at registrar level and remain registrars as a "staff grade" for many years/decades.