The IPO was about 7 times oversubscribed, leading to theoretically a big jump in share price today and the next few days. Because it was so oversubscribed, it's been more complex on deciding how to allocate the shares. Smaller investors who applied for up to £10,000 worth will receive just £749.10 worth, which is actually less than the original minimal application value of £750. The big investors who applied for more than £10,000 will get ... nothing. So they'll have to buy on the secondary market if they still want them, again implying a rocketing early price.
This morning, the shares will open at 420p. Currently, the shares are already 412p on the grey market (trading futures etc.) so, we'll just have to see what the physical shares are at by the time I get back from school, when I'll write more on Royal Mail.
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