So many red flags. Sauces, lots of them, described as creamy; semi-sun-dried tomatoes, the flagship ingredient of 1990s pastas; and truffle-infused sticky balsamic vinegar. Please, please, say it ain’t so.

Birraz, at the top end of Oxford Street, is a casual affair. Bustling. Energetic. Its cooking is, well, interesting.

The day we reviewed it was hosting a 90th birthday party in its large back room, and it was going off. The worst offenders were the nonagenarian nonnas. Quite a few of the old dears were liquored up and looking for a party. You have to love Italians: they never stop living la dolce vita.

Every now and then one or two would totter past on their sticks and walking frames on the way to the loo and engage us in jokes and comments and sparkly eyed humour. We couldn’t understand a thing. They all spoke Italian. We got the idea though. These ladies were out to par-tay. They made our day.

Birraz’s menu is large by modern standards. There were sections for cold tapas, hot tapas, fried tapas (a reminder: this is an Italian restaurant), an entire salads section, nine pastas, seven “big plates” and sides.

The “half-shell scallop marinated with truffle and taleggio gratin” read like a disaster. It was. It was also a lie. None of the small and cheap scallops were sitting on the half shell as the menu description would have us believe.

Instead, they sat forlornly in a slick puddle of white-coloured watery sauce, which tasted of salt and not much else. Pointless. Small blessings: it might have tasted of taleggio as advertised. Credit to the chef. The scallops were undercooked. Good. Some were raw. Bad. Expectations dashed. As dishes go, it was like going to a massage parlour for a sad ending.

Crumbed prawns looked and tasted like a pre-crumbed, frozen food service product. They were so sloppily thrown into the fryer – direct from the freezer perhaps – that quite a few remained stuck together. They were beyond sun-tanned, more like that dark, dark trendy furniture colour of the nineties, wenge wood.

Given all their cooking it was no surprise that any moisture these butterflied pellets of prawn might once have had, had been comprehensively driven away. They were DOA. Perhaps they should have been delivered to the table in a hearse.

A plate of antipasti was beyond all comprehension. The cheeses were okay, especially a chilli-flavoured cheese we had not seen before. Slices of mortadella put the mort back into salami.

They were as ancient as the pharaohs, a little crusty around the edges and going grey in patches. Slices of bresaola staunchly refused to taste of dried beef, no matter how hard we tried to detect it.

A small bowl of olives in the middle of the platter was indescribably vinegary. Note to chef: if you’re buying cheap olives in brine, rinse them well then drop them into a container of olive oil for service.

Two slices of “toasted” bread were revolting, dry, mealy, crumbling under the influence of their age and old enough to get a pension. Stale bread is good for toasting. Prehistoric bread, not so much.

We weren’t the only ones struggling.

At the next table four women were sharing lunch. When their food arrived, there was a lot of silent staring at the plates. After a forkful, one was heard to say – with quiet resignation – “It’s nothing like my Nonna used to make.”

Our two pastas arrived. Bucatini al tartufo was a ripper. The pasta was properly al dente. The sausage and mushroom sauce was first-rate. It had been emulsified with pan juices and grated parmesan and seasoned well.

The sausage was a little gristly and tough, but fair bump, play on. Fusilli alla Siciliana was also well-cooked and well-flavoured. Strips of smoky, seared eggplant were up to scratch. Its tomato ragu sauce was straightforward and well-tasty.

A glass of Soave – the white wine native to Venice – was one-dimensional and nothing like the complex, dry and fruit-driven DOC Castel Cerino we had enjoyed the week before at Garum in the city. Birraz’s by-the-glass list is a joke.

We shared a lamentable factory-made dessert, ice cream in a sort of cannoli pastry, and ordered a coffee that never came.

We couldn’t get out of Birraz fast enough.

Thank god for the Nonnas.