A couple who strayed onto mudflats as they walked their dog in a country park had to be winched to safety by an RAF helicopter.They called for help from a mobile phone after becoming stuck waist-deep in mud at Cudmore Grove Country Park, East Mersea, Essex.Charlotte Lomas and boyfriend Luke praised PC Shaun Hammond, the first on the scene, who knew the area well and located them quickly.The pair were walking Miss Lomas's greyhound, Chip, when they found themselves in a grassy area and her partner soon found himself waist-deep in mud.Miss Lomas went to help, but ended up getting stuck herself.