I've just been on the phone with CS trying to upgrade from VIP20 to VIP50 for just the £20 activation fee (and the £5.x pm extra) but they were adamant there would be a £35 installation fee too. Even reading to her, verbatim, what Mark Wilkin had posted on their support forum and referencing this thread, both the girl I spoke to & her manager insisted they'd have to charge an installation fee and that "the offer has probably run out".
I asked to be transferred to Retentions whereby the helpful chap there had everything sorted within ten minutes and an appointment booked for the 31st.