(For a Reuters live blog on U.S., UK and European stock markets, click LIVE/ or type LIVE/ in a news window) * FTSE 100 up 1.5%, FTSE 250 adds 0.8% Dec 29 (Reuters) - UK shares rallied on Tuesday as investors returned from a long weekend to cheer a post-Brexit trade deal that averted a chaotic finale to the tortuous divorce. The blue-chip FTSE 100 index gained 1.5% in early trading and was on course for its biggest percentage gain in four weeks, while the domestically focussed FTSE 250 index climbed 0.8% to hit its highest level since Feb. 25. With UK markets closed on Friday and Monday for Christmas and Boxing Day respectively, investors took heart from the confirmation last week of a Brexit trade deal. AstraZeneca rose 4.3% to give the biggest boost to the FTSE 100, while shares in other international firms such as Unilever and Diageo gained despite a firming pound. (Reporting by Shivani Kumaresan in Bengaluru; Editing by Subhranshu Sahu)