WARSAW, Sept 29 (Reuters) - Polish headline inflation slowed in September to a single-digit rate for the first time since early 2022, preliminary data from the statistics office showed on Friday, supporting bets the central bank would again cut interest rates next week.

Inflation reached 8.2% year-on-year in September, below a forecast of 8.5%, while the month-on-month drop was deeper than expected, according to the flash data.

The National Bank of Poland (NBP) meets next Wednesday for the first time since delivering a shock 75-basis-point rate cut earlier this month and coming just before Oct. 15 parliamentary elections.

The bank had said its bigger-than-expected rate cut in September was because inflation was slowing steadily.

"Today's CPI reading, lower not only than average market expectations, but also lower than the NBP president's indications from the beginning of this month... will most likely encourage the majority in the Monetary Policy Council to reduce interest rates again next week," Chief Economist at Bank Pocztowy Monika Kurtek wrote in a note.

Kurtek said lower fuel prices were the main reason for the drop but that the pace of disinflation would slow in upcoming months due to stabilising base effects, seasonally higher food prices and a "highly probable" rebound in fuel prices.

Fuel prices in September declined 7% year-on-year and 3.1% on the month, despite rising crude oil prices in global markets and a weaker zloty, amid allegations that state-owned refiner Orlen was artificially suppressing gasoline prices ahead of the elections.

The zloty is trading more than 3% weaker since the rate cut, while interest rate markets are pricing a cut next week.

Polish central bank Governor Adam Glapinski told PAP Biznes last week that scope for further rate cuts had narrowed "although it will continue to appear with incoming data".

Erste Group Bank said it also expected a slower drop in inflation in the coming months, but September data backed market pricing.

"This sharp decline in prices will provide further support for another rate cut, possibly between 25 and 50bps," it said.

(Reporting by Karol Badohal and Pawel Florkiewicz in Warsaw; editing by Miral Fahmy)