I'm no legal expert. Are you? Common sense dictates that it isn't illegal. Publicly funded corporations and organisations have long-standing impartiality clauses. I'd be very surprised if these were discovered to be illegal after all these decades of their usage. The civil service serves the Government and the population. The civil servants support whatever political party is in Government in an impartial way. They're not allowed to get political. The BBC is a publicly funded broadcaster. The funding comes from license payers of all political backgrounds. So the BBC stays impartial. It's not a difficult concept.
There's no such thing as free speech unless you're speaking to yourself in a darkened room. Apart from that there's always the audience and the context to consider. We all tailor our speech depending on who is present, unless we have a serious personality disorder. All we say has to be within the law - the actual law I mean; not laws you've invented to retrospectively forbid impartiality clauses for the convenience of this debate. If you are working for the MOD or the Armed Forces or the civil service you will be bound by the Official Secrets Act. This Act impinges on your free speech.
In the hierarchy of free-speech constraints, one down from the law is rules. Someone working for a company developing a product can't go about blabbing about the product when it's in development and when its commercially sensitive. They will have agreed to a confidentiality clause. But that would limit the free speech of an employee surely? Well - yes, but there's no such thing a pure free speech. When you take money off an employer there's rules. When you contract with an organisation and take their money, there's rules and obligations on both sides.
Lineker is the face of BBC Sport. He has a responsibility to the BBC to remain impartial and not bring the corporation into disrepute. He hasn't stayed impartial, and arguably he's brought the BBC into disrepute by using inflammatory comments referencing the Nazis. He's a grade A bell-end in my opinion, but my opinion matters not a jot. What's pertinent is whether the BBC will turn a blind eye, or enforce their impartiality rule. We will see.
I'm not a legal expert but ive spent thirty years writing (with lawyers) contracts, NDA's, confidentiality agreements for both sides of the equation, and regularly write corproate policy dcouments for major institutions and occasionally governments, so i can speak from a modicum of understanding. Common sense dictates absolutely . . . . . nothing. Impartiality clauses determine actions not opinions, it is overreach when they try to determine opinions.
Firstly you're conflating free public expression of opinions and beliefs with the control of information, the two are very different. The official secrets act is (or should be) exclusively concerned with the control of classified and security related and other confidential information, the overreach of the authorities has frequently stepped into control of opinions through the act, Blair's administration was particularly egregious. NDA's and confidentiality agreements in the corporate world are simple controls on disseminating information either about products, methods, systems IP etc as a protection mechanism - the fact that confidentaility agreements and the like can step into controlling opinions should be a concern to us all.
Companies and the wealthy also have the stupid UK libel laws to control the free expression of opinions, which a fair few on this forum have been subjected to by the previous scum bag owners of the club.
The BBC has a charter to be impartial in its delivery of content, but it cant even do that in any practical terms. a programme like HIGNFY is constantly critical of government and expresses opinions that are usually not countered at the time. If impartiality, the way the BBC manages it, was to apply for every joke they do about the government they should do an equivalent one about the opposition.
The UK civil service has to be impartial in its delivery of government policy, and you are right about civil servants above clerical grade cannot be political or politically impartial in their personal lives as well (which again is an overreach (in my opinion)) but the codes of conduct also accepts that very senior civil servants may have to be both politically active and not impartial as part of their duties, its not cut and dry, and is probably implemented arbitrarily. The governments overreach here has been challenged but the UK government has the right to ignore many rules that ordinary companies and citizens are subject to. The military is likely going to have to change its policy on freedom of expression as the current blanket gagging policies are being challenged in the UK courts.
Recent changes in application of law determine that "great weight must be given to freedom of expression" and legislative opinion from 2014 states that generally speaking, employees must have the right to express themselves, providing it does not infringe on their employment and/or is outside the work context”. The BBC's guidelines on the expression of personal opinions would under those legal opinions be by any lay terms an overreach of the employment contract, but the laws are so badly written that overreach by organisations to limit free speech isnt clear cut. Just because the BBC is partially public funded (and i think that there is a good argument for it to not be) it should not mean that employees and contractors should sacrifice all of their personal rights, or be limited in how they express themselves, unless of course it is in soliciting or enciting violence or other criminality.
I cannot see how Lineker's tweets have bought the BBC into disrepute, its a personal opinion based on activities the current administration is implementing or trying to implement which are also being criticised by the UN and many other international rights organisations. The incompetence and outright bigotry being displayed by many in government (with due reference to immigration issues) does however bring the whole of the UK government in disrepute, and that can be demonstrated by the lack of credibility that the UK now has on the international stage.
The irony is that many new freedom of expression laws are coming in or being ammended to protect right leaning viewpoints from hate speech legislation - but of course they only want their opinions expressed.
To conflate the expression of opinions with serious personality disorder is truly ridiculous. You might not want to openly say your other half is fat for the sake of harmony in the homestead, but saying it in certain contexts doesn't mean you have a personality disorder, the honest dissemination of the opinion might be because of reasonably held health concerns for said other half. Holding racist and bigoted opinions towards groups of people might however be a sign of psychological disorder, stemming maybe from indoctrination or unsubstantiated fear, or it might just be a lack of education or intelligence.