It can’t be easy having Andy Murray as a younger brother. Britain’s No 1 tennis player is notoriously stroppy and prone to racket abuse; he once incurred a fine of $2,500 for hurling insults at an umpire. Clearly he was never going to respect the rules of sibling hierarchy for long.

Jamie Murray, 22, the elder by a little more than a year, can still remember the humiliation of the first few childhood defeats on court. He soon accepted that his younger brother was rapidly outpacing him; what he couldn’t stomach was the gloating. Asked to describe an incident that sums up their childhood relationship, he recalls: “We’d both been at an under-10s tournament in Solihull. Andy ended up winning and he was just going nuts. On the minibus home he was winding me up. His hand was resting on the armrest and I just punched his hand. I caught his nail and broke it. Later it fell off.

“It’s never really grown back properly,” he adds sheepishly.

Last week the brothers were at each other’s throat again, with Jamie criticising Andy’s withdrawal from Britain’s Davis Cup team because of a knee injury: “If he really wanted to push himself he could have made it.”

Andy fired back with: “If he knew what it was like playing three five-set matches in a row on clay, maybe he’d understand my position a little bit better.” Ouch.

Without Andy’s much-needed presence, the British team now faces a play-off in September for the chance to remain in the World Group, the top 16 nations, for next year’s cup. But Jamie insists there are no hard feelings. “He’s our top player and we really need him but I can’t tell him what to do. He’ll make up his own mind,” he says.

Last summer Jamie managed to steal the limelight unexpectedly, and in spectacular fashion, by becoming the first Briton to win a Wimbledon title for more than 20 years. It was in the mixed doubles – his partner was Jelena Jankovic, from Serbia – and it was his first Grand Slam victory, something Andy has yet to achieve. It must have felt like sweet revenge. “Well, it’s a lot more difficult in singles,” Jamie says. “There’s no jealousy now.”

The Murrays grew up in Dunblane, where their mother, a former Scottish national coach, teaches tennis. They picked up a racket shortly after they could walk and have both had their hearts set on the game ever since: “There was never anything else we wanted to do.”

Despite the tiffs, the siblings are now flatmates. For the brief periods when they are in Britain, they share Andy’s flat in Wandsworth, south London. Parked outside is Andy’s new two-seater Mercedes. “He’s only had about two driving lessons, though, so he can’t actually drive it,” Jamie says, laughing. “His girlfriend [Kim Sears, daughter of Nigel Sears, the tennis coach] drives it instead.”

Jamie, by contrast, claims no interest in flashy sports cars – “I don’t even know what Mercedes Andy’s is, if I’m totally honest.” He’d prefer “something like a VW Golf maybe, like my mum has. I spent half my childhood being driven around from one match or training session to another, so I don’t really like being in cars too much”.

Even so, he is learning to drive, in a modest Renault Clio, and looks as though he’s going to beat Andy to his licence. “I was about ready to take my test but then I’ve just been away so much,” he says. “My gran hates me for it. She’s right: I should drive by now. She’s paid for the lessons as well, so there’s pressure to get the driving test passed – and to get my hair cut as well.”

Attractive in a gangly, mop-headed way, his nickname is “Stretch” because of his long arms (he’s 6ft 3in) and ability to lurch across court for seemingly unwinnable balls. Currently single, he denies there was anything going on, bar a little mild flirtation, with Jankovic. The on-court chemistry was instant, though (enhanced, Jankovic joked, by her offering kisses in exchange for winning shots). “We weren’t planning to play together but she arrived at Wimbledon at the same time as me, I saw her getting out of her car and I just asked her on the spur of the moment,” he says. “I don’t know why she said yes but I knew she was a really good player and we ended up winning the tournament.”

He’s keen to play with Jankovic again at Wimbledon this summer. “We’ve kept in touch. I’ll definitely ask her. We’ve texted and stuff . . . not every day or anything!” he exclaims quickly, anxious not to spark any more rumours.

The prize money for doubles is a lot less than for singles but he claims not to mind: “I’m not that materialistic and I love the life I lead.” He acknowledges that singles is by far the tougher game physically but says doubles presents different challenges. “It’s a lot more tactical,” he asserts. “There’s a lot more analysing how you play together and analysing how other partnerships play.”

So Andy’s the brawn and he’s the brains? “I don’t know about that,” he says, laughing again. “Andy’s a clever player. I haven’t played him for years. He’d beat me pretty fast now, so there wouldn’t be any argument.”

Do they ever mention that mutilated fingernail? “Actually, we were joking about it just the other day,” he says.

So, next time Andy’s lining up his killer serve, look closely at the middle finger of his right hand. You might just be able to make out the scars of sibling rivalry.

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