Gloucester's Guinness Premiership title ambitions will be put to the test in two out of the next three matches if they are forced to battle on without three scrum-halves.

Talented youngster Dave Lewis is unlikely to play again this season after he suffered a broken ankle – and underwent surgery on Saturday night – following a robust tackle by Chris Hala'Ufia during the club's stunning victory over London Irish.

Dean Ryan may have been joking when he pointed at his assistant coach and former Scotland No 9 Bryan Redpath but Gloucester are desperate for scrum-halves.

Should Rory Lawson and Gareth Cooper be needed for Scotland and Wales in the Six Nations Championship, the Cherry and Whites will only be left with 18-year-old Academy No 9 Jordi Pasqualin for important home league matches with title rivals Sale and Bath on February 14 and 28.

Fly-half Ryan Lamb, who deputised for the unfortunate Lewis with Lawson already replaced, didn't put a foot wrong against the Exiles. He will play a waiting game to see if he is needed for the No 9 shirt in the coming weeks.

"I am hoping to play. I don't care where it is – it could be at fly-half, scrum-half or inside centre," said Lamb.

"I am happy to be out there and I was pleased to get 20 minutes today.

"We also have Jordi. He's played a couple of times this season. He's a good player and he'll be a bit angry if I get picked ahead of him. We will see how it goes over the next couple of weeks.

"I was very nervous to start off with. I have played there a couple of times at England age group level – but it is only a handful of times.

"But I came on – I didn't know a lot of the moves – and most of it was through instinct. It went well.

"I had to keep to the basics and not do anything out of the ordinary.

"It is devastating for Dave. He had England Under-20s coming up and everything had been going well for him here."

A scrum-half crisis was the last thing on Gloucester's minds when the Exiles established an easy 15-0 lead through tries from wings Adam Thompstone and Topsy Ojo, fly-half Peter Hewat adding a conversion and a penalty.

Having been dumped out of Europe following back-to-back defeats, the hosts were suffering from a Heineken Cup hangover.

The forwards gave plenty of gusto but struggled in the tight against an Irish pack that better controlled their aggression.

But the arrival of specialist packmen – prop Nick Wood, second-row Marco Bortolami and openside Andy Hazell plus Irish's withdrawal of prop Tonga Lea'aetoa – changed the nature of the game.

The more the match went on, the more the Exiles were hanging on and the stronger Gloucester became.

Forgotten English back Olly Barkley kept the hosts in touch with six penalties in a near faultless display from the former Bath playmaker.

Even when they were reduced to 14 men with centre Anthony Allen in the sin bin just before the hour mark, Gloucester won that 10-minute period 6-3.

When Allen returned, Irish were a man down after centre Seilala Mapusua was yellow-carded for not rolling away from the tackle. The Cherry and Whites seized their chance.

The pack took the Exiles defence one way before the backs spun the ball to the right wing for Iain Balshaw to stroll over and touch down in the 73rd minute to clinch victory and send the hosts top of the Premiership.

"To come out of a top-of-the-table clash in the way we did in the last few minutes was fantastic," added Lamb.

"The boys finished the match strongly. After the last few weeks maybe our character and mental strength had been tested."

Gloucester: W Walker; I Balshaw, H Trinder, A Allen, J Simpson-Daniel; O Barkley, R Lawson (D Lewis 48, R Lamb 51); A Dickinson (N Wood 62), O Azam (capt), G Somerville, A Eustace (M Bortolami 71), A Brown, A Strokosch, A Satala (A Hazell 43), G Delve. Reps not used: A Titterall, M Foster.

Scorers: Try – Balshaw. Pens – Barkley 6. Yellow card – Allen (58, not rolling away).

London Irish: D Armitage; T Ojo, E Seveali'i, S Mapusua, A Thompstone; P Hewat (M Catt 74), P Hodgson; C Dermody, D Paice (D Coetzee 71), T Lea'aetoa (R Skuse 49, A Corbisiero 77), N Kennedy (J Hudson 71), B Casey (capt), R Thorpe, D Danaher (G Johnson 39), C Hala'Ufia. Rep not used: A Lalanne.

Scorers: Tries – Thompstone, Ojo. Con – Hewat. Pens – Hewat 3. Yellow card – Mapasua (70, not rolling away).

Referee: D Pearson (Northumberland). Att: 13,974.