UPDATE 1-Emerging markets trade fairs boost Reed, UBM

* UBM top 20 events 12-month forward bookings up 21 pct

* Reed's LexisNexis legal and professional returns to growth

* Both companies reiterate 2011 guidance

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LONDON, April 19 (Reuters) - Professional media companies Reed Elsevier (REL.L)(ELSN.AS) and United Business Media (UBM.L) gave positive outlooks on Tuesday bolstered by their strong trade fairs businesses, especially in emerging markets.

Reed, which runs the world's biggest exhibitions business including last week's London Book Fair, said annual shows held in the first quarter averaged mid- to high-single-digit revenue growth rates, a trend it said it expected to continue.

It also said underlying sales at its legal and professional division had returned to growth in the first quarter, helped by strong sales in the United States, although law firms, corporations and governments continued to spend cautiously.

UBM reported underlying first-quarter growth of 16 percent in events, and said forward bookings for its top 20 events in the next 12 months were up 21 percent. "We remain on track to meet our expectations for the full year," it said.

Reed said all its businesses had shown underlying revenue growth in the first quarter, excluding the effect of biennial shows not taking place this year.

The Anglo-Dutch company also publishes academic and legal products -- its LexisNexis legal business competes with Thomson Reuters' (TRI.TO) Westlaw -- and sells data and analytics to insurance companies and governments.

"We expect in 2011 a gradual recovery and a continued improvement in performance," Reed said.

Britain's UBM reported 8 percent underlying sales growth to 238 million pounds ($386 million) for the first quarter and a 19 percent increase in adjusted operating profit to 44.6 million pounds, boosting its margin to 19 percent from 18 percent.

Reed shares have fallen 1 percent this year, broadly in line with the wider market, but UBM has fallen 20 percent since March 1, when the company said increased investments in its data, distribution and online businesses were squeezing margins.

(Reporting by Georgina Prodhan; Editing by Erica Billingham)