The unrest and subsequent ousting of President Hosni Mubarak in Egypt is already proving a game-changer in terms of the Egypt-Israel peace agreement.

Throughout the three decades since the treaty there has been a widespread feeling in Egypt that the country's honour is violated by the prohibition on it sending troops into Sinai. Demilitarisation was one of the key clauses.

In late January, Egypt sent two battalions, amounting to 800 troops, into Sinai with Israel's blessing.

Large parts of the Sinai are lawless at the best of times; populated by Bedouins who expect to live autonomously and view government rules as unacceptable interference in their lifestyle. There is widespread smuggling, of people to Israel, and goods - including weapons - to Gaza.

When the unrest was at its height, Egyptian authorities thought that if the scenes they saw from their windows were really happening in urban centres where troops circulate, anything could happen in the remote and troopless Sinai.

Jerusalem officials desperately need calm in Sinai

As far as Israel is concerned, with Hizbollah in Lebanon and the Iranian-aligned President Bashar Assad in Syria, it has quite enough headaches on its borders. Watching Gaza transform into a Hamas mini-state has made it even warier than in the past about instability on its doorstep. So, after three decades of a demilitarised Sinai, Egypt had new reasons for stationing troops there, and Israel had new circumstances which compelled it to agree.

A few days after the deployment, Egypt asked for Israeli approval to send more troops, and Israel responded with a resolute no. But it seems that interference with Israel's energy supply made defence officials reconsider. On February 5, apparently following an attack, there was an explosion in a Sinai gas terminal which is part of the network that delivers gas to Israel, stopping supply for more than a fortnight. Last week, Israel agreed to Egypt deploying several hundred more troops.

Israel views the deployments as temporary - in place until stability is restored in Egypt. But the troops are now a reality on the ground, and likely to be there for quite some time before Israel decides that Egypt is stable. Regardless of the circumstances in which they were deployed, when Israel asks them to leave it is likely to be presented in the mainstream Egyptian media and perceived by the general population as a concession to Israel.

At the moment, officials in Jerusalem desperately need the calm in Sinai that only troops can deliver. But the last thing they need a few months down the line, just as we are starting to get a sense of where the country's future leaders will stand on Israel, is the welling of anti-Israel sentiment which the request to restore demilitarisation could cause.