Can my wife visit me in the UK before we apply for a Spouse Visa?

Should [someone] lie to immigration

No. Never. Do not even think of it. Absolutely not. Worst idea in the world. If you are found to be lying -- and trust me, the immigration folks are good at that -- then lying alone can be reason to deny entry.

Remember, the most important skill an immigration officer can have is being able to sniff out a liar. While we know your lie would be in good intentions (ah, l'amor, no?) they don't see it that way. Now unless your wife has professional training in espionage, she's probably not going to be a good enough liar to get through immigration control.

Almost every time I've been through immigration, I've been asked a question that I can say with 100% certainty is on the screen in front of the agent. They're looking for your reactions to the questions just as much as they are looking for the answers.

And in an age of ever-more-connected systems between governments (particularly western governments) there's a rather good chance they already know that you two are married!! So even if your new wife practices well enough to get through the questioning and maintain the bluff, they might have the fact that she's lying right in front of them. At that point, you can kiss any visa hopes goodbye.

And even if she was good enough to bluff it, AND they don't have the connected systems, AND it never comes up in questioning, there's still the moral argument to be made. Do you want to put her in that situation? Do you want to make her lie for that?

Look, I've been in a very similar situation. During the immigration process my wife and I were separated for months (and she had our child with her too, so I was missing her too!!) But we made it work. We skyped, we texted, we called. You make it work. If you're going to spend your life with her, maybe you get 50 years together. Do you really want to risk those 50 years because you couldn't settle for 49?

Do the smart thing. Don't lie to an Immigration Officer.

They can and will deny entry if they think you may intend to stay longer the visa you arrived on. I am a British citizen and my Australian wife of 8 years was denied a British visa. I earned twice the income threshold for spouse visa in the UK but was denied because she entered as a visitor and we changed our plans and wanted to stay in the UK and we had 7 days to leave the UK with no right of appeal in the UK. We are now back in Australian and still in shock at the outcome (4 months later) and probably more significantly the lack of rights to appeal etc in the UK.

I am British citizen but I am not allowed to live in the UK.

We had to give the Home Office my wife's passport while the application so we could travel internationally while the application was in progress.