The real UK barometer that's showing bruising losses for equities

A lesser-quoted barometer for the U.K. economy is currently highlighting the bruising losses for investors following the surprise leave vote in the referendum on Friday.

The FTSE 250 Index (FTSE International: .FTMC) consists of the 101st to the 350th largest companies listed on the London Stock Exchange in terms of capitalization.

It's seen in the investment community as a better barometer for the U.K. with many firms on the FTSE 100 (FTSE International: .FTSE) being multinationals, such as large mining firms that operate in China.

The FTSE 250 was down 6 percent in early afternoon trade on Monday after losses of 7.2 percent on Friday. The global sell-off is widely regarded as the worst seen since the Lehman crash of 2008.

The mid-cap index hit its lowest since late 2014 on Monday afternoon with consumer cyclicals leading the losses. British banking company OneSavings Bank (London Stock Exchange: OSB-GB) was the worst performer, down 27 percent. Housebuilders like Redrow (London Stock Exchange: RDW-GB) and Bellway (: @BWYLFDC16J-GB) also suffered heavy losses amid uncertainty over the country's future relationship with the EU.

"The collapse in equity prices in the U.K. and Europe on Friday was ugly and shares have dropped further today," Julian Jessop, the chief global economist at Capital Economics, said in a research note.

However, he added that equities had rallied strongly ahead of the U.K. referendum result which has accentuated the move.

"Friday's collapse in the FTSE 100 simply reversed that move, leaving equities little changed over the week. Even now, the FTSE 100 is still above its mid-June lows. Admittedly, the more domestically oriented FTSE 250 has fallen further, but it rebounded from similar levels in February."

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