* FTSE 100 flat at close
* GKN leads on report company might split
* CRH seals deal with Ash Grove Cement
* Rebuffed Mediclinic bid drives Spire higher
* Profit warning slashes Pendragon's shares (Recasts, adds detail and updates prices)
LONDON, Oct 23 (Reuters) - Declines among British banks and Mediclinic shares kept gains in check on the UK's main share index on Monday, though engineering group GKN was a bright spot.
The FTSE 100 closed flat at 7,524.45 points, while the FTSE 250 index of mid-range stocks, which hit a record high last week, retreated 0.1 percent.
Profit warnings in the UK market have multiplied in recent weeks, and the latest to cut expectations were car dealership Pendragon and lighting products maker Dialight, sending their shares down 15 to 18 percent.
Banks were the biggest weight among large-caps, with HSBC , Standard Chartered, RBS and Barclays all down 0.1 to 1 percent, tracking a slide in European bank stocks as political uncertainty over Catalonia weighed.
Engineering group GKN led large-cap gainers, however, up more than 5 percent after a report the company was considering splitting its aerospace and auto component divisions into two separately listed firms.
The firm was also boosted by an upgrade to "hold" from "sell" by Liberum analysts, who said disposals, a declining pension deficit and new management improving free cash flow could all push GKN's shares higher.
Construction firm CRH gained 1 percent after U.S.-based Ash Grove Cement approved its $3.5 billion bid for the firm.
"Confirmation of Ash Grove's approval means that CRH will now acquire the fifth-largest U.S. cement producer," said Davy Research analysts. "The deal is a real coup for CRH," they added, saying it would reduce CRH's dependence on third-party providers.
Among mid-caps, Spire Healthcare soared more than 15 percent, its biggest-ever one-day gain, after it rebuffed a full takeover offer from its largest shareholder Mediclinic. The South African private healthcare provider fell 2.7 percent, the top FTSE 100 faller.
Car dealership chain Pendragon plummeted more than 18 percent after saying full-year profit would not meet previous guidance, blaming falling demand for new cars creating a price correction in the used car market.
Shares in rival car dealerships Inchcape and Lookers were down 2.6 and 8.1 percent respectively.
Industrial lighting products maker Dialight also sank, closing 15.3 percent lower after it cut its full-year earnings expectations, citing short-term production challenges.
Profit warnings for UK companies have jumped to 75 in the third quarter, the biggest quarterly rise in nearly six years, consultancy EY reported.
Pierre Bose, head of European equity strategy at Credit Suisse, said more profit warnings from UK companies were to be expected if the economy's growth continued to deteriorate.
"We need results on the Brexit talks because from a corporate perspective, for investment spending, you need better clarity," Bose added.
In a note, Credit Suisse said that despite the UK market benefiting from a global cyclical upturn, it faces significant economic and political challenges. The bank remains neutral on UK equities.
"The UK is obviously that much more sentiment driven, Brexit focused and currency focused," said Bose, pointing to slower economic growth, inflation and an absence of wage growth weighing on the market. (Reporting by Kit Rees; Editing by David Holmes)