Our much-missed member-on-sabbatical, Gayot Fow, has answered this on his blog. With permission, and for the benefit of the OP, I post the text of his answer here.
Essentially the OP wants to purchase a house in the UK to attend cultural events and otherwise enjoy the offerings of this island. The OP understands that the 6 month Standard Visitor Visa (SVV) works for visa nationals and that the equivalent 6 months leave-to-enter (LTE) works for non-visa nationals. The OP wants to know if there’s another type of visa available to covers this, and if a long-term visa might be more appropriate.
First of all, there are lots of people that do this sort of thing, i.e., purchase a house or flat and then show up during the social season and maybe for a few weeks in the summer. I used to help them ‘back in the old days’ and can attest that it’s not a rare situation at all.
Without any doubt there is no other type of visa available other than the SVV/LTE mentioned above. They do not have a ‘rich person’s visa’ or a ‘house owner visa’. They used to have a “Retired Person of Independent Means” visa, but it was discontinued in 2010. And moreover, creating a new kind of visa like that isn’t going to happen, at least until the Brexit severance is complete, and even then I doubt it.
Over on the tiered side of the visa world, there’s various investor visas, but these are settlement visas and the OP’s intention is not to settle here. It might work up until the first leg of the investor visa expires and then they see that the OP has been visiting all along and hence abused the visa by deception. That’s a bad thing. Say goodbye and don’t expect to be back for a while.
Returning to the topic, the OP in this case wants to have smooth transits through UK immigration controls when they arrive even though they are (presumably American) and do not normally require visas.
There is only one answer to that: get an entry clearance. Even though you may not need one, an entry clearance saves wasted air fares and the distress of removal from port.
The entry clearance in this case is an SVV. And the OP wants to know if there are long-term SVV’s available. The answer is ‘yes’, but they are hard to get without a solid performance history and an impeccable premise. Having a vacation home might be a great premise, but they will continue to issue 6 month SVV’s until they see 3 – 5 years of performance. After that they will issue a 2 or 5 or 10 year SVV.
NOTE: having a 2 or 5 or 10 year SVV does not mean the person can stay for that period of time. No matter what kind of visa the person has they cannot stay longer than 6 months on any single occasion.
NOTE: “LTE” means ‘leave-to-enter’. It’s the stamp one gets when presenting a non-visa national passport, like American, Canadian, Australian, and so on.
NOTE: there are about half-a-dozen UK solicitors who have built up a reputable practice area in helping ‘high net worth’ individuals. It may be worthwhile instructing one of these alongside your house purchasing solicitor. The house purchasing solicitor, for example, will need to notify the Bank of England that a large amount of money is coming through and get permission from them to clear it; whereas the immigration solicitor, on the other hand, will know how to present your premise and explain your bank transactions. You won’t find both skills in a single individual, but you will have good luck locating a firm that offers both high-net-worth immigration and real-estate specialities. I can think of 3 offhand and I’m guessing there’s at least double that number of firms out there.