<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<asp:Timer ID="Timer1" runat="server" Interval="500" OnTick="Timer1_Tick"></asp:Timer>
<asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
</ContentTemplate>
<Triggers>
    <asp:AsyncPostBackTrigger ControlID="Button1" />
    <asp:AsyncPostBackTrigger ControlID="Timer1" />
</Triggers>

<asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Push Me"/>

public static int testing;

protected void Button1_Click(object sender, EventArgs e) {
    //Initialise static
    testing = 0;

    var progress = new Progress<int>(ProgressReport);
    Task t = new Task(() => Test(progress));
    t.Start();
 }

public void ProgressReport(int progress)
{
    //Update the static with the current progress value
    testing = progress;
}

public void Test(IProgress<int> progress)
{
    for (int i = 0; i < 10; i++)
    {
        //Pretend to do something intensive
        Thread.Sleep(1000);
        //Output the progress
        progress.Report(i);
    }
}

protected void Timer1_Tick(object sender, EventArgs e)
{
    //Output the value of the static to the label
    Label1.Text = testing.ToString();
}