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* FTSE 100 down 0.3%, FTSE 250 off 0.2%

Aug 7 (Reuters) - The UK's exporter-heavy FTSE 100 index dipped at open on Monday, weighed down by heavyweight miners, while shares of Unite Group fell to the bottom of the index after a rating downgrade.

The FTSE 100 index edged 0.3% lower at 0712 GMT. The index logged a weekly loss on Friday, snapping a three-week winning streak.

Last week investors assessed a widely expected quarter percentage point rate hike from the Bank of England, data pointing to slowing business activity across Europe and a surprise U.S. credit rating cut.

The industrial metals and mining sector fell 0.7% on the day, tracking a decline in copper prices.

Shares of students accommodation provider Unite Group slipped 1.8% to the bottom of the FTSE 100 after RBC Capital Markets cut its rating to 'sector perform' from 'outperform'.

The midcap FTSE 250 index dipped 0.2%. (Reporting by Shreyashi Sanyal in Bengaluru; editing by Eileen Soreng)