If you really want to learn about pharmacology, you would get more out of doing medicine and intercalating in it than you would out of doing the first year and then transferring out. The first year course will be basic science on a similar kind of level to the medicine course, rather than the more advanced research-based pharm stuff you would do in an intercalated degree (which would generally be equivalent to doing a 3rd year pharm course). Intercalating would also give you an extra degree, whereas doing a first year and transferring out won't give you anything for your CV/FPAS application. If you're really into pharmacology then do the whole degree and think about grad medicine, but this is much harder to get into. IMO, the best option for combining the two would be to do medicine and intercalate in pharmacology. I did this, though for different reasons.
Also, just to clarify for some other people in the thread, a degree in pharmacology does not make you a pharmacist - it's a different subject from pharmacy.