Lecithin is derived from unrefined soya oil and is likely to contain allergenic proteins. Although the risk of a severe reaction may be small, if you are allergic to soya, it may be best to play safe and avoid products containing lecithin. Hydrolysed vegetable protein, which is used as a flavouring, does not have to be declared by source. The source is most likely to be soya or wheat, but there is a small possibility it could be peanut. There has been no research into the implications of HVP for allergy sufferers.
Different retailers operate different policies.
Sainsbury, for example, always declares the source of HVP if it is peanut. Other companies may not. It is technically possible for these ingredients to be derived from peanut oil, although it's highly unlikely. Even if peanut oil was the source, the risk of an allergic reaction would be extremely low because the oil would have been refined. Because of the dangers, desensitisation is rarely undertaken and only in the hands of one or two experts.