UPDATE 1-Big Yellow says cautiously optimistic

* Occupancy levels up 3 pct quarter-on-quarter

* Revenue down 6 pct year-on-year, but trend improving

* Says cautiously optimistic

(Adds detail)

LONDON, July 7 (Reuters) - British self-storage firm Big Yellow Group (BYG.L) said on Tuesday that trading conditions continued to improve in the first quarter, with a 3 percent higher occupancy level at June 30 against March 31.

The group, which has 55 stores and a further 15 in development, said same-store occupancy at June 30 was 71.5 percent, up from 70.9 percent at March 31 but down from 77.5 percent a year ago.

Total store revenue improved 1 percent quarter-on-quarter to 13.5 million pounds ($22 million), but was 6 percent down on the same period a year ago.

Chief Executive James Gibson said trading conditions had continued to improve. "We anticipate the usual seasonal slowdown in the autumn and continuing cyclical uncertainty but remain more cautiously optimistic," he said in a statement. (Reporting by Paul Sandle; Editing by Dan Lalor) ($1=.6161 Pound)