I had an almost identical experience at Manchester on August 19th 1985, also involving a B757-200 (GBLVH) on a MAN-CFU-MAN. As we rotated on Rwy 24 a flock of herring gulls rose up from the grass and five were ingested into the right engine. There were no bangs, but the vibration readings went off the clock and flight deck filled with a strong fishy smell. We shut down the engine, declared an emergency and held at Barton to burn off fuel, when the cabin crew served breakfast. Total flight time was one hour. Six or seven fan blades were found to be buckled. As there was no other damage to the RB211 the engineers fitted a new fan assembly and the flight departed that evening. Three days later our incident was overshadowed by the British Airtours 737 disaster. I remember a municipal rubbish tip close to the airport came in for a considerable amount of flack for attracting seagulls!