Try something like this:
Private Sub txtsurcharges_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtsurcharges.TextChanged
Dim c As Double 'It is bad to use integers for currency, as integers cut off decimals.'
Dim surcharges As Double
Dim total As Double 'We also need to remove the £ char.'
If Double.TryParse(txtsurcharges.Text.Replace("£", ""), surcharges) = False Then
'It looks like it isnt possible to parse the string, probably because there is some special character or letter.'
'Some type of error handling will go here. (MsgBox or something else)'
End If
If Double.TryParse(txttotal.Text.Replace("£", ""), total) = False Then
'It looks like it isnt possible to parse the string, probably because there is some special character or letter.'
'Some type of error handling will go here. (MsgBox or something else)'
End If
c = surcharges + total
txttotal.Text = "£" & CStr(c)
End Sub
Hope this helps.