Sorry I can't help with VB coding to do this but you can always set up a Custom Slide Show and have one custom show within the file setup to show the "pound" slides and another to show the "euro" slides and then the presenter just needs to select which "show" they are presenting before they begin.

Go to the Slide Show tab and choose Custom Slide Show. Then create NEW and include all the slides related to the first currency. Repeat the process and create another NEW show to include slides related to the second currency. You can then move between the two all within the one PPT file.

Let me know if you require further assistance.