In answer to your original question, you may contact the MHRA who may be able to give you more specific information. They can be contacted here:
http://www.mhra.gov.uk/Contactus/index.htm
The MHRA oversee the licensing of all products in the UK and will only allow a product to be classed as a medicine and allow it to be administered after proven clinical trials have taken place. They may be able to give you specific information about the use of E124 and EDTA as pharmaceutical ingredients.
I suspect though as the product you are alluding to does have a product license, they will refer you back to the manufacturer.
All medicines contain ingredients called exipients in addition to the active drug. They are usually necessary to mask the taste or colour. Some exipients are neccesary to ensure that the drug is absorbed in the body correctly - this is the case for the EDTA in your preparation. Unfortunately, there is a risk that some people can be allergic to these. These risks would have been scrutinised during the trial phase before the medcine was put forward for a license.
There are many products that contain exipients - as an example some shampoos and bubble baths contain EDTA. The colour E124 can be found in many products available without prescription - such as Germolene cream. They can also be found in foods such as Jelly Tots.
If you are suspicious that somebody has had a reaction to a prescrobed product it is essential that it is reported to either your GP or pharmacist who can raise the problem with the manufacturer.