You could try to go private, but it might be expensive if you are not a patient. The local BUPA hospital wanted £60,000 from me for a year of herceptin before it was on the NHS, partly because they were billing for my oncologist, even though he was donating his time to his 'highest-risk her2-positive patient.' If you could get it privately through something like healthcare at home, it would be cheaper (since they administer outside of a hospital, they don't need to pay VAT).
Another option might be to look into trials via
http://www.clinicaltrials.gov, which should have all of the GSK trials in Britain, since the company has publicly committed itself to putting all of its trials into this database, as well as some others.
There is a Genentech trial, for example, in which participants get either T-DM1 or Capecitabine + Lapatinib
http://www.clinicaltrials.gov/ct2/sh...U%3AGB&rank=17
There are, of course, participation criteria, but it might be worth considering since these two options both seem very good.