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* FTSE 100 slips ahead of Fed, BoE policy meetings

* Goldman Sachs cuts forecast for BoE's terminal rate

* Mondi jumps on its Russian plant sale

* FTSE 100 slips 0.1%, FTSE 250 falls 0.5%

Sept 18 (Reuters) - UK's FTSE 100 slipped on Monday in choppy trading as investors awaited key central bank interest rate decisions this week, while shares of Mondi rose after the paper and packaging firm agreed to sell its largest plant in Russia.

The exporter-heavy FTSE 100 was down 0.1% by 0823 GMT, while the mid-cap FTSE 250 declined 0.5%.

The focus remained on the U.S. Federal Reserve's and the Bank of England's policy decisions as well as key domestic inflation data later this week as the market hoped for an end to the monetary tightening cycle.

The BoE may hike rates by 25 basis points (bps) to 5.5% on Thursday, possibly the last hurrah for one of the great tightening cycles of the last 100 years.

"The consensus is that the BoE will hike again and inflation is proving a bit more stubborn. I still think that a lot of the impact of monetary tightening hasn't yet fed through," said Richard Flax, chief investment officer at Moneyfarm.

Also, Goldman Sachs lowered its forecast for the BoE's terminal rate by 25 bps to 5.5%.

Rate-sensitive housebuilder stocks dropped 1.2%.

Britain's main manufacturing trade body cut its forecast for the sector's growth for this year and next, citing a sharp fall in factory output and economic uncertainty.

Mondi Plc rose 4.6% as it agreed to sell its largest plant in Russia to a unit of Moscow-based real estate developer Sezar Group for 80 billion roubles ($825.7 million) in cash.

Shares of online grocer Ocado Group rose 7.1% to the top of the benchmark index after brokerage Jefferies raised the stock's price target.

Phoenix Group shares rose 0.9% with the life insurer expecting 2023 cash generation to come in at the top end of its forecast range.

Marks & Spencer climbed 2.2% as the retailer stock started trading on the FTSE 100, after being promoted in September.

(Reporting by Siddarth S in Bengaluru; Editing by Savio D'Souza and Sohini Goswami)