<asp:RegularExpressionValidator
ControlToValidate="txtMobile"
ErrorMessage="The mobile number is incorrect! The number has to start with 07 and may not contain more than 12 digits."
ValidationExpression="07\d{6,10}"
Display="Dynamic"
Runat="server" />
<asp:RegularExpressionValidator
ControlToValidate="txtEmail"
ErrorMessage="The email adress is incorrect."
ValidationExpression="^[A-Za-z0-9._%-]+@[A-Za-z0-9._%-]+\.[A-Za-z0-9._%-]{2,4}$"
Runat="server"
Display="Dynamic" />