Is the LycaMobile 2000 min & 9G data for £18 offer too good to be true ? Unfortunately YES they will disconnect you when tethering !
…Lycamobile reserves the right to withdraw or suspend the offer or to disconnect you if we suspect that offer is being used for commercial purposes, for conferencing, or if it is not being used in a handset (in a SIM box for example), if it is being used for tethering…
If you are not tethering then you may want to buy it !
For PAYG deals that DO allow tethering check out