Do budget networks actually get slower data speeds?

Hi AskUK,

I am in London and looking at SIM only deals from budget mobile networks like giffgaff, iD Mobile, Lebara, SMARTY, VOXI and similar.

I often see people say that these networks get lower priority or slower speeds compared to the main networks, especially at busy times. But it is hard to tell what is real experience and what is just online speculation.

So I wanted to ask people who actually use them day to day.

Have you personally noticed slower data speeds on these networks
Does it mainly happen in the evenings or during commuting hours
Is it worse in central London compared to outer areas
If you have used both a budget network and the main network, did you notice a difference

I am not worried about coverage or price, mainly interested in how usable mobile data feels in real life in London.

Would really appreciate hearing real experiences rather than marketing claims. Thanks in advance.