She would never be so vulgar, but the Countess of Mar could advance a claim to be Britain’s grandest aristocrat. An ancestor may have paid up to bag the family earldom, but if so the secret died with Alexander I of Scotland, who awarded the gong back in 1115 — making Mar’s the oldest title in the House of Lords.

Not that the countess’s current seat glints with baronial splendour. Rather than a drawbridge, one passes two bungalows before reaching her whitewashed cottage from where she and hubbie run a small goat farm in the golden Worcestershire hills. But this rural idyll is illusory. The countess is fighting a ferocious battle against Britain’s chaotic immigration system. After 21 years she has resigned from the panel hearing immigration appeal cases, claiming the whole system has descended into an “expensive legalistic game”.

She has a mass of horror stories from her two decades on the Immigration Appeal Tribunal (which two years ago became the Asylum and Immigration Tribunal): secret amnesties being granted to illegal immigrants without public consultation; adjudicators drawing salaries but hearing no cases; disreputable lawyers spinning out cases for up to 14 years; a vast factory in Bangkok, known to British immigration staff, producing fake British passports “to order”; entire terminals at Heathrow left without immigration officers . . .

Oh, and if proof were needed that hell hath no fury like a woman who has stalked out of a job, she lobs one hell of a salvo at her former boss on the appeal tribunal, Sir Henry Hodge. There is obviously no love lost between them. Mar scurries off to find Hodge’s two-line acceptance of her resignation but returns empty-handed. “I must,” she thunders “have thrown it away in disgust.”

Still, for all her steel, Mar is not the conventional aristocrat. In her floral dress she looks less Harpers than Hyacinth (Bucket). Her two coronets sit in a 1950s-style glass cabinet and her voice betrays no haughtiness, reflecting a life spent working as a nurse, BT inspector and lately herdswoman.

The family estate was confiscated yonks ago, but she betrays no bitterness. “Oh, think of all the liabilities,” she smiles. Mar shows me portraits of her ancestors, including 30 earls, now crammed onto her tiny landing. They range from a bloke who ran Scotland to a fascist homosexual who lived with his black boyfriend in an Ealing basement.

Many Mar men seem to have had a bit of a ’mare: they either went mad or got shot. But Mar matrons are more formidable: Lady Frances was an original “bluestocking”, the group of women intellectuals who eschewed flippant society chatter; Lady Rachel forced some poor toff to marry her at pistol-point. The current countess is up to hubbie number three, a charming concert pianist. “You have to spend a lot of time looking,” she laughs, “before you find the right one.”

Her independent spirit — recognised when she topped a poll of hereditaries to remain in the upper house — shines through when madam deputy speaker assesses the Lords. “I think it is accepted among peers that some have bought their peerages,” she says casually, “although that has probably always been the case. Where it has gone to the dogs in the last 10 years is we have got a lot of people who have lost an election (to the Commons). Why should we get the dross?” If you think that spirited, wait for her view of the appeal tribunal. “I don’t tolerate fools gladly,” she says, appraising me over the floral teacups. “I just grew irritated. The management of the tribunal got so bad. It is an appalling con. My conscience could no longer stand it.” Relations with Hodge nosedived last Christmas. “I had a huge stand-up row with him,” she says.

“He had been in post, in the same building, since the previous April and had not once come to see us (members of the panel). He floated into this meeting, made a speech and was about to disappear and I just let fly. I told him how desperately unhappy we all were and that we didn’t know what we were meant to be doing.”

Just when you think you have Mar’s measure as a ferocious rightwinger, she comes over all cuddly right-on. She recalls how she refused to sit with another member. “He announced he was going to ‘chuck out’ an applicant as he was probably the one who daubed paint on Churchill’s statue.” This followed riots in Parliament Square, but Mar insists there was no evidence linking the immigrant to the incident. “I told him if he continued like that I would go to the president.”

Since her resignation she has been contacted by Migration Watch and far-right parties hailing her as the flower of Scotland and the saviour of Britain, but this appals her. She favours controlled immigration and sympathises with those seeking a better life here; she simply objects to political deceit and administrative chaos. Ministers, she believes, have been too weak to make the case for immigration so have pretended it is not taking place. The result? Public cynicism, which could lead to civil unrest.

“We need the truth about the number of immigrants.” But she adds: “I hope we don’t ever end immigration. This country has thrived on it. What I would say is, ‘Come here, get a job in six weeks, don’t claim benefits or expect chronic illnesses treated and don’t bring your family, keep to our laws. And you come in with an ID card. After a while you will be allowed to settle’.”

Despite government denials, she suggests an amnesty for illegals already here is inevitable. “How can they cope with a backlog of 450,000?” Intriguingly, she says this has secretly been tried before. “We keep having amnesties,” she laughs. “I know of at least two: one at the time of the Balkan war and another in the 1980s.”