UK's FTSE 100 weighed down by Lloyds after health check

* Lloyds falls after only narrowly European bank test

* Aggreko (LSE: AGK.L - news) falls after fellow power supplier's profit warning

* FTSE flat after rebounding off 15-month lows last week (Adds quote, detail)

By Alistair Smout

EDINBURGH, Oct 27 (Reuters) - A fall in Lloyds Banking Group weighed on Britain's top equity index on Monday, after Lloyds only narrowly passed a regulatory health check for Europe's banks.

Lloyds was the worst-performing FTSE 100 stock in percentage terms, falling 2.4 percent. Lloyds just passed a test to determine whether it had enough capital to weather another economic crash, calling into question when it will resume paying dividends.

Overall, roughly one in five of the euro zone's top lenders failed the health checks at the end of last year, but most have since repaired their finances, the European Central Bank said on Sunday.

Lloyds was the most heavily traded stock on the FTSE 100 relative to its average, trading nearly its 90-day average volume just two-and-a-half hours into the session.

"Large numbers of investors are involved in Lloyds and are looking for them to start paying a dividend at some point, but the more money that is needed to bolster their balance sheet, the less there is for dividends," Manoj Ladwa, the head of trading at TJM Partners, said.

"Especially when the UK seems to be moving ahead of Europe's economy, the expectation is that UK banks would've performed better than European ones. But Lloyds is a concern."

Just behind Lloyds on the list of declining FTSE stocks was Aggreko, down 2.3 percent. Traders cited a profit warning by fellow emergency-power supplier APR Energy (Other OTC: APRYF - news) .

Britain's blue-chip FTSE 100 index was flat at 6,386.57 points by 1149 GMT, after managing a slight rebound last week from the 15-month lows it reached earlier in October.

The FTSE 100 hit a peak of 6,904.86 points at the start of September, its highest since early 2000, before slumping in October.

Markus Huber, senior sales trader at Peregrine & Black, said some traders may be tempted to book profits on last week's rebound.

"Overall sentiment remains positive. However, with markets having risen sharply over the past week, some profit taking would be in order," Huber said. (Additional reporting by Sudip Kar-Gupta)