It's not so much the universities not allowing transfers directly into the final year, it's the professional bodies that require a certain period of study at the awarding university.
When you talk about your masters you don't specify whether its an MEng or MSc. The MEng (120 credits at L7) is treated as an undergraduate course for all 4 years and thus, universities will not be to forthcoming in allowing you to transfer in, with the new funding implications (my university are not taking any direct entries from home/EU students this coming year for any point of entry other than Year 1!!!). With an MSc (180 credits at L7) it's a postgraduate programme and transfers in are easy to organise.