* FTSE 100 up 0.7 pct at close
* Posts monthly loss as European bourses gain
* Carillion falls 20 pct after another warning (Recasts, adds details, updates prices at close)
LONDON, Sept 29 (Reuters) - Britain's FTSE signed off September with a monthly loss on Friday, underperforming continental peers in a month that saw sterling shoot to its highest level since the Brexit vote.
The FTSE 100 index ended Friday's session 0.7 percent higher at 7,372.76 points, however, as GDP data showing that UK growth slowed to a four-year low in the second quarter put pressure on sterling on the day.
While the disappointing GDP data stoked doubts as to whether the Bank of England would raise rates at its next meeting in November, recent hawkish rhetoric from the central bank has supported the pound.
This has hampered British blue chips, many of which source their revenues overseas. The FTSE posted a loss of nearly 1 percent for September.
Sterling slumped in the immediate aftermath of the June 2016 Brexit vote to leave the European Union, which gave dollar-earners an accounting-related boost.
"The rebound in sterling has acted as a bit of a drag on the UK benchmark," Michael Hewson, chief market analyst at CMC Markets UK, said, noting the symmetry with the pound, which is on track for its best month against the dollar since 2013.
Analysts have also pointed out that investor sentiment regarding the UK market has soured. Societe Generale, for instance, has cut its UK position in its multi-asset portfolio to zero.
On the day, financials, consumer stocks and miners contributed the most to gains.
Glencore, Rio Tinto, BHP Billiton and Anglo American were up between 0.7 and 2.6 percent.
Oil majors were in positive territory as oil prices boosted the sector, with Royal Dutch Shell and BP both up 0.3 percent.
Both Brent and U.S. crude are set to chalk up another weekly gain as investors bet that efforts to cut a global glut are working and that the demand outlook is improving.
ITV was the biggest individual gainer, rising more than 3.5 percent after Barclays raised its rating on the stock to "overweight" and said advertising was improving in the UK.
Insurer Beazley jumped 4.3 percent after it reckoned its losses from hurricanes Harvey, Irma and Maria and a series of earthquakes in Mexico would reduce its 2017 earnings by about $150 million, less than analysts had earlier expected.
Among smaller stocks, British construction and support services group Carillion plunged 20 percent after it warned it expected full-year results to be lower than market forecasts, as it booked a further provision relating to services contracts.
(Reporting by Julien Ponthus and Kit Rees; Editing by Catherine Evans)