Superb, excellent, great, etc. 'Lovely Jubbly' was originally an advertising slogan for 'Jubbly', a triangular-shaped frozen orange drink which was popular in the 1950s and 60s. Later popularised by the character 'Del Boy' in British comedy 'Only fools and Horses'.
Rodney: "'Ere Del Boy, geezer over there says he'll give you a pony for the Betamax video recorder if you throw in a case of that Yugoslavian Scotch."
Del: "Lovely Jubbly!"