(ShareCast News) - The largest UK banks face several further operational headwinds which the market may not be fully factoring in yet, analysts believe.Foremost among those is the 2018 implementation of the IFRS9 accounting standard regarding provisions, which will be half again as high as IAS39. That will reduce those lenders' Tier1 equity ratios by 70 basis points. On average, their tangible net asset values will be cut by 6%, although StanChart and Lloyds Banking Group will be the most affected, analysts at Exane BNP Paribas said.Near-term dividend expectations may also be impacted, the analysts led by Jonathan Pierce explained in a research note sent to clients.The Bank of England is also expected to require large UK banks to hold MREL at a level broadly equivalent to twice the Basel total capital requirement. That could reduce earnings per share by between 3-6% across the space. On this score, HSBC was expected to be the most affected.As if that were not enough, higher interest rates would not be as beneficial for banks as many believe.Challenger banks might also be held to lower MREL requirements, the broker said.On the basis of all of the above, Exane downgraded shares of Barclays to underperform from neutral and those of Lloyds to neutral from outperform. Their target prices were cut by 10% and 9% to 260p and 82p, respectively.StanChart on the other hand was kept at underperform, although the target price on its stock was slashed by 22% to 700p.HSBC and RBS were kept at neutral. The target on the stock of the former was lowered 11% to 540p while that for the latter was kept at 360p.None of the target prices incorporated the potential for additional provisions related to the Susan Plevin case, the broker added.