The lego shop doesn't usually do discount codes. They have 20% off on Friends and city at the mo but offer is changing tomorrow.
If it's a non exclusive set you'd probably get it at least 20% cheaper everywhere else anyway. For exclusive sets you may get it in Smyths using a code for there but most of their deals were done weeks ago.
The 'VIP' loyalty scheme is a £5 voucher once you've spent £100 which is better than most. But you have to spend £100 to get one. They also often do free sets with a certain spend on certain themes. But the actual prices tend to be higher than other places. As mentioned, the "exclusives" can often be found elsewhere too.