Nursery is Group Care, if with 3-5's then 3:24 ratio is not unusual (3 adults to 24 children). There are other adults around for backup and support.
Nannying is 1:4, 1:3, 1:2, 1:1 or to put another way 1:'number of children in family'. There are no other adults around for backup or support, unless a parent at home.
Nursery experience is experience, it is relevent for nannying, but isn't the same as nanny experience. The experience it brings to nannying is things such as the Educational aspect, planning activities.
When working on a lower ratio, with no other adults, as every parent knows it's a long day, without any break! There's no lunch break! Nannies are based within a private home which is a lot different to a nursery, there may just not be the same facilities available. At nursery, they often have a cook, so a nursery nurse may not know how to cook!
Most nursery workers I expect do have some 'sole charge' experience... in the form of babysitting. Especially if they have done daytime babysitting at weekends.
With childcare, it's all about the range of experience someone has. The more experience in different settings - nursery, pre-school, after-school club/youth group, in-home - someone has, the better they should be able to cope with anything that comes up in their work in childcare.
With regard to training, I feel that some agencies do not understand the various types of training currently available. It can be hard to find out what a particular couse has consisted of, if it was practical or only theory based etc. CACHE are improving the amount of information they provide about their courses, but I find it hard to find the same level of info from other examination boards. Therefore when talking about training, agencies should be asking a lot about what the training was and how it was done, so that they understand better about how it is relevant to different childcare jobs.
Just my view of course