Had two sets of shots of the same bird, but sadly not enough of the left hand side of the ring.
The letters look like part of Museum (I can see Museu), part of London (don) and start of SW7 I believe (SW). So a BTO ring and probably ringed in the UK.
The numbers I can make out are are (1)780, with the (1) being somewhat in question. So around 3 digits short.