I've looked into the new rules and I don't think the GGUK guidance is quite accurate. My understanding is this:
Guide groups that manage their own premises have always been required to have a PRS licence if they use music that is registered with the PRS (this will be most music except "traditional" songs or music that is no longer in copyright. The cost of this is 1% of the building's income.
From January 2012 Guide groups that manage their own premises will also be required to have a PPL licence if they use any recorded music (i.e. other than live performance). The cost of this is 1% of the building's income or £42 if the building's income is less than £10,000 a year.
Both fees will be collected together under one joint licence adminstered by the PRS, but the fee for the PPL licence is in addition to the PRS licence fee. This means that halls with an income over £10,000 will be paying twice as much.
If your unit/district manages its own building and already has a PRS licence then the PRS will contact you automatically when it is time to renew, so you don't need to do anything until you hear from them. If your unit/district manages its own building and does not have a PRS licence, then you need to think about whether music is used in the building (by Guides or anyone else) and whether you need to have a licence (you can give the PRS a call if you are not sure).
This only applies where you have your own premises. Community buildings are required to have the licence themselves if their community group hirers (like Guide units) use music, so units using those buildings will be covered by their licence. Again, if you are not sure whether it is your responsibility or the people whose hall you are using you can give the PRS a call.
This is my interpretation of the rules (having spent considerable time on the phone to the PRS). I think I'll email GGUK as I don't think this is clear from their guidance.
HTH