You are not allowed to fast on Eid day any other day would fit. On the other hand some madhabs recommend not to fast six consecutive days to make a clear difference between voluntary fast and ramadan.
According to the European council for fatwa and research (ECFR) today (Tuesday, the 5th Juli, 2016) is Eid in Europe. Of course this is wrong from the point of view of a local sighting as the used calculation method is based on a global sighting anywhere on earth and the moon would only be visible tonight in the northern parts of our planet, while yesterday it was only possible to see it in some southern parts. This is only the 2nd time since I'm in Europe that we fast 29 days and ironically both times were wrong (from the view of local view and according moonsighting.com the last time also for the global) as Muslims in Europe mostly or before this fatwa of the ECFR followed the Saudis who are always fasting one day too early (from the point of view of a local sighting for Saudi Arabia itself) with a sighting error vacancy rate of around 96 % according to independent astronomers (As a reference read articles and sighting reports of moonsighting.com). Note that this percentage only represents the error for three months namely Ramadan, Shawwal and dhi-l-Hijjah (the most important months due to the worship which must he exercised during them). So you have two options for when to start: fast beginning with the 2nd day of Shawwal according your mosque leaving the sin or responsibility to those people who have made the decision whom they would follow when fasting or breaking the fast or use the internet check sites like moondighting.com and take the most accurate calculation and follow it in that case if there's an error it's only on your responsibility as you might have left the jama'a with your fast or breaking fast.
Note this year ironically Saudis have made a correct decision even if they follow there um-al-Qora calendar while pretending they do a moon sighting (a more correct statement is that they allow sighting reports while relaying on the calendar). So you may start fasting from Thursday on.
Therefore one or a community must decide:
- Are we following the view of a global sighting anywhere on earth? -> in that case Eid was on Tuesday (in Europe).
- Are we following a local sighting? -> Than following the Saudis is wrong as Allah said
[He is] Lord of the two sunrises and Lord of the two sunsets. 55:17
which means each two different locations have different sunrises and sunsets, so maybe at one place the moon might be seen on sunset while on the other not (and this is what counts in fiqh, as if you saw the moon later the hijri day would have started so that moon would count for the next day, you have only a narrow time gap to make an accurate sighting). And the longitude and the geographical distance between Saudi Arabia and UK is of couple of hours difference, which means a major difference in this matter.
According to moonsighting.com: A sighting on Tuesday, the 5th Juli, 2016 (in UK) would be only possible with optical aid. So maybe Eid is Wednesday (if sighting was really possible) or on Thursday, the 6th Juli, 2016 as at sunset on Wednesday a crescent moon must be clearly visible.
See also in my major reference.
And Allah knows best!