Reserving a table at Margaret Thatcher's place . . .

When Britain's best-known grocer's daughter goes to the people on June 9, she can be sure that one particular voter will be hoping for a Conservative victory as fervently as she.

The voter is canny property developer, Rodney Cloke, who in the spirit of Thatcherite enterprise recently transformed the grocer's shop once owned by Mrs. Thatcher's father into a restaurant for the local upper crust. It is not hard to appreciate Mr. Cloke's point of view: the effect of a Labour victory on his venture's profits is almost too terrible to think about.

Mrs. Thatcher (then Margaret Hilda Roberts) was born in the town of Grantham, Lincolnshire (which was dubbed, in a recent radio poll, ''the most boring town in Britain'') above the thriving grocer's shop. And it was here as a schoolgirl helping out behind the counter that she first learned the virtues of thrift and hard work which, during the past four years of Conservative rule, no Briton has been allowed to forget.

But the prime minister's birthplace - in its heyday, a model of middle-class respectability - had been lying derelict for some years when Mr. Cloke spotted its commercial potential. He could not afford to delay. As the local paper reported, tourists were spiriting away bricks and rubble from the building to take home as souvenirs.

Mr. Cloke refurbished the Victorian house, turning it into a 48-seat restaurant of considerable splendor (with prices to match), and named it, after much deliberation, ''The Premier.'' Mr. Cloke, who is reticent about his own political affiliations, insists that the restaurant is a historical rather than political monument.

Even the choice of the name ''The Premier,'' he says, was the result of political caution. Other suggestions, like ''Blue Angel'' and ''The Right Bite, '' which might have brought charges of political bias, were discarded - as was the idea of decorating the walls with photos of the Iron Lady.

The first customers to cross The Premier's threshold were some local Conservative Party activists holding an official function. Tom Scott, chairman of the Grantham Area Conservative Association and a former mayor of the town, could hardly find the words to express his enthusiasm.

He loved it all: the replica of the door of No. 10 Downing Street that leads into the restaurant lounge, the standard English fare, and the miniature dispatch box that contained the bill. He had a few words of praise for Mrs. Thatcher, too:

''I admire her immensely, because she's straightforward, doesn't beat about the bush.''

He added, ''I nipped upstairs during dinner to see the room where she was born. It was so small, you wouldn't believe. Just goes to prove you can come from a lowly background and still reach the top.''

Mrs. Thatcher herself has yet to eat at The Premier, although she has been invited. Nor could she attend the ceremony last February at which the local Conservative MP, Douglas Hogg, unveiled a blue plaque on the outside of the building to commemorate the birthplace of Grantham's most famous daughter. She did, however, take time to write and express her gratitude.

Among those who do not frequent the restaurant and have no plans to, is Lloyd Ramsden, leader of the Labour group on Grantham's council. ''It's certainly no attraction as far as Labour-minded people are concerned,'' he said. ''Who wants to be fed politics when they go out for a meal?''

In fact the only time Mrs. Thatcher's opponents did frequent the building was just before Mr. Cloke took it over. Seeing it as a symbol of Thatcherism, they often used it as the backdrop for demonstrations against her economic policies.

Mr. Cloke chose to recreate the store as it would have looked in the 1930s, when Margaret Hilda, a young teenager, was most closely involved in helping run the business under her father's watchful eye.

The prices on display in the shop are those that customers would have paid in the 1930s and The Premier's management can boast that it's the only corner shop in Britain where prices are permanently frozen. Were it not for the fact that none of the goods is for sale anymore, this would appeal no end to the 12 percent of Grantham residents who are unemployed. It might even persuade them to change their political allegiances.

As it is, most of the people of Grantham will be voting for Labour in the June election, as they have done for many years. But because Grantham forms part of a parliamentary constituency that includes affluent farmers and other traditionally Conservative voters, the region is likely to remain Conservative. Both Mrs. Thatcher and Mr. Cloke, it seems, can rest easy about her immediate political future.