So, the Daily Mail is criticising Nick Clegg for not being "British enough".
This particular line of racism is one that's shown up in US politics a lot recently. I expected we'd have to wait (probably several decades, at the current rate) for a BME leader of a major political party before seeing it here.
Of course, it's not surprising that racism itself is being used. Partisans for all UK political parties, including the "left" or "progressive" ones, are happy to use all kinds of privilege-based and stereotype-based slurs and metaphors - racist, sexist, ablist, etc. - against their political opponents, without thinking about the wider effect this has on either the usefulness or trustworthiness of their party's anti-discrimination policies.
The attack itself will probably do more harm than good, this time. The Lib Dems jumped from 20% to 30% in the polls largely based on reminders that they existed. It's quite possible that the attacks on them, combined with the existing "underdog" narrative, will push them even higher, not lower.