Thanks @MArkWilliams and @frank for your prompt replies. I did suspect the 50 character limit of the existing system to be insufficient.
@frank (or @MArkWilliams), would you be able point to which documentation you are referring to? I of course tried searching for this information on the Companies House pages before posting, but was unable to find anything specifically for this. The documentation might be useful for any other queries I may have.
Also thanks for pointing out the alphanumerics, fortunately mechanisms that will maintain this data in the existing system support the use of alphanumeric text.