said by AVonGauss:
... Sounds more like a case of I found out the value route is working just as well for me at a lower cost and I want to use the lower cost option. ...
Actually the premium rates for UK landlines are lower ($0.0070) than the value rates ($0.0079).
I put in a ticket for this problem too as I was quite often getting a 503 (call rejected) from my ATA for premium routes to the UK, but the value routes were working reliably. It's apparently fixed, but I'm waiting a while before re-instating the least-cost routing rule in my dial plan.