Could I have deformed the wheel of my new bike by being too heavy?
220 pounds (100kg) is not that heavy.

At £459 or about US$600 retail, the Saracen is also not an inexpensive bike. It should be more than able to handle your weight unless you're doing very aggressive biking (such as hopping on and off curbs or doing wild jumps without the proper technique). Riding on rough roads is well within the design parameters of this "hybrid" bike.

If your wheels are deforming**, it is likely either a manufacturing defect in the rim or your spokes were not properly adjusted/checked by the dealer. As @Orb notes, you should have also gotten a request from the dealer to come in after the first week to tighten things up as part of the new bike service. I would immediately go back and demand that it be fixed or replaced. I would myself insist on new wheels and insist that the spoke tension and hubs be properly checked before they are reinstalled.

** Note that I'm assuming your wheel (the metal bits) are deforming. Your description is vague. If your tire (the rubber bits) is bulging, then that could be caused by a local weakness in the tire wall. In either case, take it back to the shop to get it replaced.

The UK has good retail trade laws so you should be well within your rights to demand resolution.

ps. I do hope you bought it from a local bike shop rather than online. It's much harder to yell at people online, I've found.